Further improve mobile layout

* Dynamic sidebar width
* Add padding so that entire sidebar is shown when scrolling is needed
  * this also applies to desktop, btw
Disable swiping on desktop
Implement asciinema plugin

Close #66
Merge pull request #175 from cormier/asciinema

Implement asciinema plugin
Rework installation instructions

- Add note on installation being optional
- Add some instruction how to create app shortcut for Chrome
Merge pull request #179 from tribut/install-notes

Rework installation instructions
Merge pull request #177 from lorenzhs/mobile

Further improve mobile layout
Focus input bar when not on mobile

This improves the UX on desktop while avoiding the virtual keyboard
popping up on touch devices
Remove trailing spaces
Replace tabs with spaces
Merge pull request #180 from tribut/nonmobile-focus

Focus input bar when not on mobile
Add nick to highlight notification from channels
Merge pull request #181 from tribut/notification-nick

Add nick to highlight notification from channels