Reduce complexity of the annotate module

[maltem-za]

Difficult to simplify. Some ideas I have here are:

1. Document, annotation collection and tagset icons should appear before the name, other icons after. Lock icon should potentially be greyed out to denote that it's not clickable, in contrast to eye icon (or should get its own space somehow).
2. Remove the + next to the "Collection currently being edited" dropdown and make that a dropdown option itself.
3. More in-context actions to work on the tagset (as mentioned in #279), possibly remove the + there and only have the three-dot menu.

Another suggestion that was made is to give the different panes slightly different background colours to make them easier to distinguish. Also relates to #214.