Panel optimizations, navbar buttons and directives refactor - arethusaGenerator

Updates to the `allMessages`, `helpPanel` and `globalSettings` panel. They all use `ngIf`, `fade` and `slide` transitions now. Looks better and is more efficient.

Navbar buttons where updated during the process - everything in there is now wrapped in a directive, which also goes for `uservoice` (fixes #391). 

An open panel is now indicated in the top-bar also - the button which opened it and should also be used to close it again is now highlighted (fixes #389)

Closes #240 - the real problems with the `revealToggle` are fixed now and its a directive that we will probably deprecate soon anyway.

A new global object `arethusaGenerator` is introduced here. We had a couple of directives that were completely the same, apart from a few variables. (all panel triggers and the directives for `history.undo` and `history.redo`).

This is completely DRY now. The `arethusaGenerator` (aliased to `aG`) generates a couple of directive definition objects. Lots of code lines saved...