Re-establish selection after link dialog runs

Any selection made in the link dialog will destroy a selection in the
editor.  Previously, we corrected for this only when we had selected a
link, but we really need to do this every time.

https://bugzilla.gnome.org/show_bug.cgi?id=736689
Tighten up parent refs in ListParameters

While working on another bug, I discovered some issues with the
maintenance of parent references for IMAP Parameters being held in
ListParameters (of which every Parameter is held).  This patch not
only tightens up references, it also verifies references are accurate
when the ListParameter is destroyed.
Don't strip trailing space from signature separator

https://bugzilla.gnome.org/show_bug.cgi?id=736985
Update to 0.8.0
Merge https://git.gnome.org/browse/geary