Editor / Improve keyword selection

[fxp]

Instead of selecting keywords in a popup, select them directly in a thesaurus widget in the editor. Improvements:

• support to easily add keyword to a previously selected thesaurus
• support CharacterString, Anchor and XLink mode (and change the mode at any time)
• keep default editing mode for free text keyword editing.

[fxp]

Dev branch: ​https://github.com/fxprunayre/core-geonetwork/commit/6fc05cd50c3c385332ecc2daba14db5acc7efdfd

[fxp]

Commit 3fc5c9049777b10d33844b949fa3a0b3c7cfebe6

[fxp]

Minor fix & improvements: master commit adaacc6785d7d8b131a7e1417ef7a760870a7412