"Glossae by commentary" filter

[mromanello]

some design changes to the filter (as discussed yesterday):

• put the filter behind a button (when not in use it stays collapsed and takes up less space)
• move the filter/button at the very top of the glossa viewer panel (column)
• make the list of available commentaries scrollable
• add a search field to make the list quickly searchable

PS: can we have in brackets, beside the commentator's name, the total number of glosses existing for the text section in focus?

[pletcher]

These kinds of search fields are always more work than they seem -- should be implemented with 1c0bf84

[pletcher]

PS: can we have in brackets, beside the commentator's name, the total number of glosses existing for the text section in focus?

This is not easy to do the way things are built right now.

[pletcher]

Counts added in ac4ffc6