Style note content edit field

Right now, rich text editing is coming through the contenteditable
attribute. I imagine this has all kinds of code injection security
concerns and it is not really working exactly right anyway. Long term,
this will have to be replaced with TinyMCE or something like that.
Add and style note toolbar buttons

These don't actually do anything yet. But, hey, they look nice...
Enable note deletion.

This was done previously in a placeholder form, but now it really works.