Settings backup/restore + small fixes

Another stepping stone for settings sync, should enable easier debug for us and manual sync solution for the impatient. Also should make wiping localstorage less of a problem since it also backs up user highlights which don't have proper UI for them.

Major:

• Changed ImportExport component into a service since it's mostly logic/direct DOM-manip, not much of markup going on, makes it more reusable and avoid mess with slots
• Implemented settings save/restore function
  • New dropdown button in modal footer: save, save with theme, restore
  • Settings saved with array version - current version [1, 0] - works similarly to semver but in array, for future-proofing it will refuse to load settings with major version != 1 (i.e. [2, 0]) but will work different minor version, i.e. [1, 1].
  • Separate control for theme saving since theme data is quite heavy.
    • For future we might add dialog box asking if user wants to import theme as well if it's present
  • Restoring goes over supported properties and updates them using setOption with data found in file. Minor stuff:
• one more fix for "p's broken theme" fucking up theme editor and making it mostly unusable
• changed "Peek"/"Close" buttons to use icons instead, feels a bit more natural and less confusing given that there are now button in footer too.
• panel footers no longer use panel header colors, it just looked silly and didn't really work with some themes (redmond), cleaned up their styles a bit

src/App.scss

@@ -547,9 +547,21 @@ main-router {
   border-radius: var(--panelRadius, $fallback--panelRadius);
 }
 
-.panel-footer {
+/* TODO Should remove timeline-footer from here when we refactor panels into
+ * separate component and utilize slots
+ */
+.panel-footer, .timeline-footer {
+  display: flex;
   border-radius: 0 0 $fallback--panelRadius $fallback--panelRadius;
   border-radius: 0 0 var(--panelRadius, $fallback--panelRadius) var(--panelRadius, $fallback--panelRadius);
+  flex: none;
+  padding: 0.6em 0.6em;
+  text-align: left;
+  line-height: 28px;
+  align-items: baseline;
+  border-width: 1px 0 0 0;
+  border-style: solid;
+  border-color: var(--border, $fallback--border);
 
   .faint {
     color: $fallback--faint;
@@ -862,16 +874,10 @@ nav {
 }
 
 .new-status-notification {
-  position:relative;
-  margin-top: -1px;
+  position: relative;
   font-size: 1.1em;
-  border-width: 1px 0 0 0;
-  border-style: solid;
-  border-color: var(--border, $fallback--border);
-  padding: 10px;
   z-index: 1;
-  background-color: $fallback--fg;
-  background-color: var(--panel, $fallback--fg);
+  flex: 1;
 }
 
 .chat-layout {