WIP: Keyboard navigation

[Bauke]

Stuff for functionality

• [x] Navigate sidebar
  • [x] Switch from topic to sidebar (and vice versa) s
  • [x] Go up/down arrow up/down
  • [x] Enter group enter
  • [x] Browse list of groups b
• [x] Add topic listing keyboard navigation
  • [x] Go up/down arrow up/down
  • [x] Go to home/end (first/last topic) home/end
  • [x] Go to next/prev page n/p
  • [x] Enter a topic
    • [x] Via topic title (topic or external article) enter
    • [x] Via comments (always to topic) c
  • [x] Vote on selected topic v
• [x] Add inside topic navigation
  • [x] Links arrow up/down to switch, enter to go to link
• [x] Add comments navigation
  • [x] Go up/down arrow up/down
  • [x] Vote (on other person's comment) v
  • [x] Reply (on other or self) r
  • [x] Edit (on self comment) e
  • [x] Delete (on self comment) d
• [ ] Add modal search stuff
  • [ ] Groups
  • [ ] Users
  • [ ] ...?
• [ ] Add an if to check if keyboard navigation is enabled before doing anything using sync

Stuff for settings entry

• [x] Add to feature_list
• [x] Add feature_enabled checkbox and setting in sync

Relevant issue: #29