Re-enable "fetch more lines" after trimming lines on buffer switch

Fixes #404
Merge pull request #442 from glowing-bear/fix-line-fetching-after-switch

Re-enable "fetch more lines" after trimming lines on buffer switch
Create dark theme by extracting theme settings from glowingbear.css

* Remove style.css as those values should be themable as well.
* Update urls in index.html to link to dark theme by default
Provide a way to change the theme in the settings

* Selected theme is dynamically loaded
* Preferred theme is stored in the settings.
* Default theme = dark
Add light theme
light-theme: darken most colors by 50% and add it to theme manager
[light theme] make the background lighter
[light theme] set highlight colour to something readable
[light theme] improve readability of default grey colours
[light theme] make default text color readable
[light theme] fix the notification colour again
themes: fix some base colours
support direct html colour specs in client messages
add pgup/pgdn keys and fix history in multiline edits
embedded content: check if scrollIntoViewIfNeeded vendor method is available
Support narrowing buffer selection with Alt+0-9 after using Alt+g or when onlyUnread is enabled, and show numeric overlays for Alt+0-9 keys on the buffers
Add support for explicit fromnick in protocol messages where availiable

This can replace the prefix-nick-guessing where available.
Support host-rendered time

If available, display the time as rendered by the host instead of own
calculation
Correct setId placement

The setId had been implemented once on the protocol instance and once
as a (unused) static method.
ignore empty messages received on websockets, which may be used as pings