Work toward making inspector persistent
Use undefined value to remove a key rather than empty string

Otherwise it is impossible to tab out of the key input of a
new tag row -- since the value is still empty, the tag is
removed before you have a chance to enter a value.
Add hover indicator in sidebar
minor adjustments to sidebar, adding mock-ups.
work on hover state.
Remove hacky overrides
Fix preset form field spacing
Rationalize CSS classes