Use flexbox when available.

Makes things actually work on firefox.
Prevent click event on sort

Unlike most browsers, firefox raises the click event even if an element
has been removed/re-inserted between mouseup/mousedown events. This
means that it was getting fired on sort.
Don't hide subsequent elements of shrunken notes.

This causes notes to be clipped in odd places (at formatting changes
etc.)
Fix syncing of note deletion

This was actually a much bigger problem. It appears that the server only
increments the version on modify, not create.

closes #96
Don't force debug mode.