improve legend / title and add a second one in dual/split map view

[robarto]

in Dual/Split view both maps need a title and legend.
the window should be a bit smaller, if possible.

[bgunt]

buttons "Themen" and "Klassen" under both maps

[nsteffens]

Addressed this in e4e1258 and 33a2b48 but getting the time slider to work in the second map will be kind of difficult without getting too much redundancy in the code. I'd suggest creating a Legend.js class where the time slider and GIF-export behavior might then also move. @felixerdy's opinion would be interesting to this since he implemented these features.

Size adjustments will follow, the question is how urgent this issue is. Should I integrate everything or do you want the basic functionality now on the website.

TL, DR: Legend on second map works, time slider not yet. Size is also still the same. Do you want this already now on the gh-pages branch or do you want to wait until everything is finished?

[felixerdy]

@nsteffens I would definitely agree on creating a seperate Legend.js class as I already thought about that. Would result in a better code structure and cleaner code.

I think the timeslider should work at least before pushing to gh-pages