Themes v2

WARNING After merging in v2 themes, reverting back to v1 will cause PleromaFE to be stuck on white screen if user had non-empty non-v1 configuration. Only workaround is to clear IndexedDB in browser, but that will remove ALL customizations, including user highlighting. !380 (closed) fixes that for develop branch.

Key points:

• In-depth customization of many aspects of theme.
• Keeping the simplicity of current pleroma-fe themes, as well as maintaining backwards compatibility with it.
• Bringing in some convenience features and fixes, like being able to have dark foreground color in a light theme and contrast text in notifications counter.
• Helpful contrast indicator to help making themes accessible.

Bugs

• keep checkboxes do not actually affect theme export despite what help text says
• "post text" in preview, along with monospace, fix input field using wrong text.
• bottom bar ('load more') - check link color.
• Reset button doesn't reset everything when v1 theme is in the localstorage.
• Some sort of bug related to user profile about input field not appearing after transition
• user profiles are FUCKED

Stuff done/need fixing

• fix tab-switcher because it causes me a great mental distress
• Per-component (?) color customization
• Opacity controls where it matters
• Panda theme support (dark panel headers on light themes)
• Auto-fixes for badly colored notifications counter
• Contrast indicators
  • Basic function
  • Hints explaining if contrast is good or bad, localization
• Better notifications unseen indicator
  • Basic function
  • Should be on a separate layer, on top of status, not below
• Drop-shadow adjustment support
  • Fix fallback not working when switching components
  • Fix tab-switcher to properly put border below inactive tabs
  • Adjustments control
  • Better styles/unification with other controls
  • Replace buttons/inputs/navbar shadows with generated ones
    • Somehow make it possible to use inset shadows on panels (header overlaps the .panel so inset shadows gets hidden)
    • Remove borders on buttons?
  • Fix button fallback (non-css-var) not having borders
• Improved preview window showcasing more elements
• v2 admin presets/some v2 themes
• Localization strings
• Roundness UI
  • Fix layout
  • Consistency with "override" checkbox like in advanced colors
• rgbo section needs minor layout fix or something
• Reset buttons
  • One that resets ALL settings to currently active theme/colors
  • One for each category that unchecks all "override" checkboxes
• Checkboxes for partially loading theme/preset (i.e. make it only import colors but not affect roundness/shadows)
• Fonts.
  • sans-serif/serif/monospace/custom selector for inputs, posts, and everything else.
  • Future-proof it so that it would be possible add more styles in-between. (server-provided fonts?)
  • "Custom" enables an input field to enter font-family name.
• some help text for shadows
• fix UI really not liking illegal/null inputs
• improve bundling v2 themes - allow using external files somehow

QA checklist:

• transition from v1 localstorage doesn't cause issues
  • roundness settings are lost (name changes)
• loading v1 user preset works
• loading v2 user preset works
• loading v1 instance preset works
• loading v2 instance preset works
  • there's one issue that v1 themes and v2 themes that lack some definitions do not reset stuff like shadows. see note 1
• clean-loading (no localstorage) doesn't cause issues
• check IE11/Edge?
  • Top bar is entirely broken but that's not related to this MR, it's been broken for a while, apparently.
  • Most checkboxes in customization do not work at all. No errors in console, no warning. They just don't work. I blame Vue and/or Edge.
  • Oh and IE11 still doesn't work.
• no major issues, no major differences between v1 and v2 generated colors

Notes

1. Picking something like Redmond XX theme and then switching to pleroma-dark would keep the win9x reliefs. This might be of annoyance, and checkboxes to keep/reset some settings might help.