GUI: move the "mark as reply" selector to the row of buttons

There's a GCI task for changing various replying modes from within the composer
(think reply-to-all vs. reply-privately). That change needs a button to be added
somewhere, so it makes sense to use a button for the feature which Thomas added
yesterday. Besides, it seems to me that it is a bit easier to discover this way.

This is best viewed as a diff from commit
944a49e33562bd508a2af6e0dcfc938ba2769f1b; that way it is clearer what has
changed compared to the standalone-checkbox approach.

v2 changes:
- Hide the button altogether when not replying instead of just disabling it.
- Pretty formatting of the tooltips and sanitization of HTML input
- Better captions

Thanks to Thomas Lübking for his comments.

v3 changes:
- Enable quick toggling via a default action, without expanding the menu
- Fix restoring of v2 drafts

v4 changes:
- Removed one superfluous QAction::trigger
- Better identifiers for the slots for updating & processing the quick toggle
action
- Changed the caption of the threaded reply marking action
- Some inline comments

REVIEW: 114815
Importing the icons for threaded/flat view from Oxygen

Sourced from format-indent-more and format-justify-fill.
GUI: use icons for message threading
Add proper credits for Yazeed Zoabi, a GCI student
Update copyright year to 2014
Handle lines starting with a period during SMTP transmission

RFC5321 specifies to prepend lines starting with a period with a
second period that is then removed by the server.

BUG: 329609
REVIEW: 114875
Fix build failure on EL6
Fix copyright year for Stephan
Fix build failure on EL6 (try #2)
Documentation about enabling the SSL compression

The change was made to earlier releases as well, so it would be cool to undo it,
but it looks like there's no API for that for Qt older than 4.8 -- so we just
cannot do anything here.
IMAP: do not assert crash on new arrivals during an in-progress FETCH

Some time ago the code was changed so that it reset the TreeItemMsgList's
fetching state back into LOADING when new arrivals were detected; this was
designed to make sure that the sync state and UIDs are always saved
consistently. Unfortunately, some other parts of the code tried ty depend on the
TreeItemMsgList already being fetched(), which is now no longer true.

Simply removing the assert works. The test case tries to check for this scenario
more aggressively, and also makes sure that we support the same not only for
part fetching, but for message metadata fetches as well.

BUG: 329757
REVIEW: 115009