Preparations for Leipzig gloss

Morph can now optionally add a gloss translation to an analyses. Right now we only store and retrieve the gloss, but don't expand our morph attributes to the full Leipzig gloss schema. A mapping dictionary is available in this PR, but not implemented yet.

Morph needs a configuration of `"gloss": true` to activate it.

Another conf option has been added: If external analyses should be preselected, one needs to add `"preselect" : true`. Not sure what the best default is here - I think I would personally go with preselect all the time, unless I specify not to. Right now it's off by default, but can be activated through the morph selection panel.

Minor issue with the gloss: It currently doesn't notify the program that a save is needed - which means that if one only updates the gloss, the save button is not enabled. I think we might get away with this for now... Usually another change will accompany this anyway.

Reason why it's not implemented yet: The input field for the gloss is real-time - we don't want to trigger events everytime we hit a key. The easiest way to delay this would be to add a submit button, but I generally like the idea of not having to use one. Needs more exploration.