Customizable themes

Implements #41 (closed), needs review and testing.

• Change how base16 rules are used globally (base01 panel-headings -> base02 for example)
• Add a theme editor in settings menu, complete with a preview
• Remove the usage of base16-theme.css files in favor of themes consisting of only 4 main colors
• Add a couple preset themes in styles.json
• Make themes persist

changed the description

added 1 commit

• a7500410 - Fix color inputs to wrap on mobile, fix timeline background color to not clash with panel headings.

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merged

mentioned in commit 9674320e