initial hack to re-order attachments
make raw search a config option

and provide access to raw/search by key sequences

Type (anywhere)
- "/" for a regular search
- ":=" for a raw search

REVIEW: 112017
pass searchline shell-a-like history

and inline completion and a history popup

REVIEW: 112018
fake linked header to allow order swapping

as last resort when sorting is not suported by the server

REVIEW: 112036
Revert "initial hack to re-order attachments"

Sorry, rebase ebkac

This reverts commit 346e18f78581afffe78cf4b213056927c0e5f479.
GUI: MessageView: show an indicator whenever the message parts are being loaded

It looks that QWebView does not have support for showing any placeholder
whenever it is loading data from network; instead, a simple empty widget is
shown. This is suboptimal because the user doesn't know that the mail is
currently loading unless they pay close attention to the global
application-level progress indicator in the status bar.

This patch propagates loadingStarted/loadingFinished signals of the enclosed
SimplePartWidget instances to the MessageView which simply shows/hides another
progress indicator.

Another idea was to implement this on the QNAM level, but it turned out that the
same MsgPartNetAccessManager is used also for attachment download which is not
what we are interested in.

REVIEW: 112092