Disable tags and related on abstracts

[dstillman]

Also drop them when switching a note to an abstract

[dstillman]

(In [1030]) Fixes #447, Disable tags and related on abstracts

New methods:

Item.removeAllRelated()
Item.removeAllTags()

Also:

• Tag selector didn't initialize properly if it was closed when Firefox was started
• Items pane would lose open state of items and current scroll position when an item was edited while the tag selector was open -- added save/rememberOpenState() and save/rememberFirstRow() to fix this, and these could also fairly easily be used to remember the open state while switching between collections