If the application binary is not installed in /usr/bin the client
with this patch considers to check the relative location
../../etc/owncloud-client/ to find the system exclude.
This is an important bit for AppImage based packages of the client,
as this runs from a temporar mountpoint and the system file can not
be found under /etc.
The avatar image is fetched from the server async, thus connect a signal
from the account if the avatar changes.
Server feature https://github.com/owncloud/core/pull/26872 is needed.
The avatar pixmap is fetched from the server by the Connectionvalidator,
once it has validated the user name, it queries the avatar pixmap.
If the server does not have the avatar route, an empty pixmap is stored.
