SVN_SILENT made messages (.desktop file)
Revert "Use qobject_cast when checking the return value via if"

As Thomas writes, using qobject_cast doesn't make any sense here:

> The check is for the verticalScrollBar() heap member
> If m_scrollParent is not a QAbstractScrollArea, this will segfault in either
> casting case.

This reverts commit 231975037aa307a0b28badfea4df97674d39858e.
Ubuntu: adds an secure connection option selector to Imap Settings

User can select connection type from an expandable option selector,
which updates the imapPort text field to the standard connection port.

User can still override port value in imapPort text field

Also we have to use QT_TR_NOOP for marking strings in list model
elements for translation and call translate on them in the
selectorDelegate. QT_TR_NOOP apparently makes the strings visible to
Qt Linguist but doesn't actually translate anything.

REVIEW: 117212
Ubuntu: fix issues with showing connection errors

Implements opening a dialog when there is either an imap or network
error

BUG: 332870
REVIEW: 117307

Also implemented imapAlertReceived to display message in dialog popup

removed pagestack.pop on imapAlert

Moved Info dialog to a seperate component
SVN_SILENT made messages (.desktop file)
cleanup: remove unreachable code
GUI: QTabBar is nicely reachable via member function
Refactor the way how we find preferred item within multipart/alternative
GUI: expand previewable attachments upon first click on the attachment icon

The motivation is to make expanding of previewable attachments smooth, but at
the same time do not interfere with the way how the button has worked so far too
much.

When an attachment cannot be previewed, nothing changes and everything works as
it used to work before.

When a preview can be shown, however, clicking on the icon of the attachment at
the time the preview is collapsed will simply show the preview. When the preview
is shown, however, clicking any part of the icon will still bring up the menu as
it used to work previously.

This is an alternative implementation to review #117068.

v2: Use another approach for determining what action to take based on the actual
state of the preview in order to prevent duplicate connections. Thanks to Thomas
Lübking for pointing out a possible problem here.

BUG: 332586
REVIEW: 117295