Independent scrollbar(s), styling of dependency Tree, bugfix in sentenceList

One step closer to the behaviour we want: The sidepanel can now be scrolled independently from the main-body. In theory the main-body should be scrollable on its own, but check the commit message of a2fdf7c.

Includes some work to the `dependencyTree` directive - the svg template is now compiled during the linking phase and not upfront. This way a user can create content around the tree canvas without touching the directive. We use it to display the settings panel, the count of unused tokens and the diff toggle.

The settings panel has been reworked and is not using buttons anymore. A sliding transition for it would be nice to have, but is of course not a top priority. During that it was also driven out to a separate template to handle the HTML stuff better.

A handy utility CSS class to make a flash-like transition has been added. (`.flash-on-hover`)

Creating a childScope for `sentenceList` was also necessary, even if it's generally unrelated to this PR. Check the commit message of 62e995f.