Minor updates to parse tree.
Merge branch 'master' of github.com:OpenPhilology/phaidra
Parse tree root nodes do not have to be 0, just the lowest head ID in a sentence.
This means that shortened sentences can be displayed in a root with a relation to a root node,
and that we wouldn't have to screw with their IDs in order to patch them back into a more complete sentence,
they can just retain their true IDs.
Merge branch 'master' of github.com:OpenPhilology/phaidra
Fixed parse tree circular dependency.
Parse tree bug fixes:
- Root correctly assigns to be the head of the parent-most element.
- Morphology/relationship label tool can be dragged around the screen without fear of losing it by dragging too quickly.
- Morphology/relationship label tool's form section will scroll if it would overflow.
Merge branch 'master' of github.com:OpenPhilology/phaidra