Add Tooltips to explain tools/options

#1

Since Subform has a lot of new (great!) tools and features, it might be helpful to have short tooltips on-hover so you know what you're clicking.

#2

@nick We agree! In fact, Kevin and I have talked a lot about taking the tooltips to the next level by showing examples/illustrations inline.

Autodesk Inventor does a nice job with this:

2017.04.17 Status update