Blender Git Loki

Drivers UI Cleanup (Part of T55145)

* Remove "Show Debug Info" option. Everyone has it turned on all the time,
since it's just useful to have
* Make the "Remove Driver" button less prominent. It doesn't happen that much,
so it shouldn't take up as much room
* Make "expressions" textbox wider (i.e. taking up the whole column width)
by separating the label and textbox on separate lines.
* Rename "Add Variable" button to make it clearer to users what "variables"
may be (i.e. they serve as a way to specify Inputs, just like adding a
"Source Data" node in a nodetree)
* Regroup buttons