Checkpoint on the way to sorting.
Drag and drop working client side and submitting new order of ids, just need an implementation server side.
Wire up calendar note reordering using optional 'note_order' attribute.

If present, overrides default reversed keys ordering.

Keep 'note_order' in sync when removing a note.

When adding a note to a calendar w/ 'note_order', append the key to it.
Add 'sendalert_default' flag to community.
Allow setting 'sendalert_default' on add / edit of a community.
Respect community's 'sendalert_default' when adding content.
Fix test breakage.
Merge branch 'calendar-notes-2-1193129'
Merge branch 'community-sendalert_default-1207087'

Conflicts:
	karl/content/views/files.py