GitLab

* Ignore vertical size hint of HTML status bar to allow the message structure
  view to grow as much as possible.
* Set minimum height of message structure view to 10 pixels. This
  allows the message structure view to shrink to a very small height.
  Allowing it to shrink to zero height is not useful because then the user
  cannot resize it anymore.

Sponsored by: Intevation GmbH

BUG: 436044
FIXED-IN: 5.18.0

BUG: 434392
FIXED-IN: 5.17.0

We need to detect the identity of a message to know, if Autocrypt is
enabled the core logic should be shared. In future we may want to add
more ways to detect the identity, like the header Delivered-To,
X-Original-To or [X-]Envelope-To. But this needs to be determined later.

To determine the idetity for a mail correctly we need to know the
current folder identity.

In order to support Autocrypt we need to know if the corresponding
identity for an email wants Autocrypt support or not.

CCBUG: 422095

CCBUG: 422095

FIXED-IN: 5.15.3
BUG: 391030