Change UI for MessageListPage.qml in Ubuntu port

REVIEW: 117028
Ubuntu: fixes for the launcher

- Switch to QCommandLineParser for argument parsing
- Fix problems with using relative paths and add option for autopilots'
  `-testability` command line arg to enable autopilot interface

REVIEW: 117030
Adding proper credits for Boren Zhang
IMAP: allow ']' when parsing an astring

The IMAP code would by mistake reject tokens that contain a resp-special
character ']' when asked for parsing astrings. This was because the of the rule:

    ATOM-CHAR       = <any CHAR except atom-specials> rule

...which confused me enough so that I ignored an explicit allowance for the
resp-specials earlier in the ASTRING-CHAR rule.

Thanks to Miguel <migtavares@gmail.com> (DeviantPeer on IRC) for reporting this.
Sorry for the trouble.

BUG: 332651
REVIEW: 117105
Installed into system locations, trojita can't be
started

This fixes not looking in standard data locations for the installed qml
files. To fix this it first checks if main.qml exists in the current
source tree, if not then we get a list of standard data locations and
try to find main.qml and throw qFatal if can't be found.

BUG: 332639
REVIEW: 117109