Additions to relation plugin

This was initially started as work on tag nesting, only two or three commits are dedicated to this, other work sits on a different branch soon to be shared.

Adds some functionality to the relation plugin - selecting tokens by relation label and making changes to multiple tokens in a single step. Features I haven't though of initially, but this could be very useful for other plugins (morphology!) as well!


Also applies some custom styling to Foundation's tabset, which are made a little more compact.