added bottom margin that appears when dragging placeholder
fixed bug where you could not use delete on a textarea
implemented couple of changes from webteam feedback:
1. "undo" button now hides itself when non-functional
2. starter "Drag a field over" copy rewritten to also suggest a click
3. instruction detail text rewritten to be a JQuery-UI tooltip
Merge branch 'gh-pages' of https://github.com/JSlote/formbuilder-rsn into gh-pages