Add dark.css

For licensing information, see the header of the file; it is *not* licensed under the UFL.
Append a newline to license and config-example
Fix Splark's name, change license to CC0

* Splark was misspelled as Splarc
* The original has been relicensed as CC0 - Public domain
Add "use dark theme" checkbox and default CSS for it

widescreen CSS still missing.

Also removes the dashed border on top of the "Frame Data" panel and moves "width: 260px" into the .framedata-sub class.
Add widescreen CSS for themes

also moves some declarations into the new CSS class "widescreen-separate".
dos2unix two remaining files

charts/index.html and css/widescreen.css were still using DOS style line endings (CRLF).
Add themes event handler.

The event handler is general: If the rules explained in the files are followed, additional themes can be added without any javascript changes!
Fix a bug when removing a theme.

I was counting upwards in a loop that started on the last element :)
This worked as long as the link to remove was the last one, but caused the browser to hang otherwise.
This could be reproduced by reloading the page while in dark theme. Firefox would keep the checkbox checked, but the theme wouldn't have been loaded. (This still needs to be fixed; it just doesn't crash the browser now.)
Execute theme event handlers once on page load

Firefox (and other browsers probably as well) keeps checkboxes' checked status when reloading a page, so their handler has to be called as well then.
Remove a lot of layout stuff from dark.css

Now all the components stay in the right place.
Remove font changes from dark.css
Remove a "black text" rule from dark.css

The text on inputs (playback speed, pause special frames, frame) was completely unreadable.
Merge pull request #138 from lucaswerkmeister/implement-134

Implement 134: A toggle button for a dark theme