Improve UI for vocabularies #238

On the page "Administration / Vocabularies" we need to improve the usability a bit:

• Each entry (=each vocabulary) should habe two buttons (use BrowseView.row_actions):
  • One for editing the Vocabulary itself
  • One for editing the list of Terms of the Vocabulary
• The list for editing the Terms should be a Browseview which only shows the Terms of a single Vocabulary
• It should be possible to edit, add and remove Terms inside that BrowseView (and return to the same BrowseView again after that)
• When adding a new Term, it should automatically be assigned the correct Vocabulary (need to change URL for the primary_button)

We did something similar in the basxconnect_crm project (ICHTHUS) for the group, where a click on a group will list all members and a member can be added, edited or removed from a certain group.