Core update
added opencv imgproc to dependencies


```
$ ./qtox 
./qtox: error while loading shared libraries: libopencv_imgproc.so.2.4: cannot open shared object file: No such file or directory
```
No border for message area (as in mockup)
Starting client activates existing instance if such exists
Added -P <profile> parameter which makes qTox start (and not activate any existing instances) and load specified profile
-P value name also translated
Merge branch 'pr851'
Merge branch 'pr854'
Merge branch 'pr855'
Update de.ts

revised all of german translation.
fixed some original translation strings
adjusted translation messages

as discusses here: https://github.com/tux3/qTox/pull/848#discussion_r20851990
Italian translation: update
Merge branch 'pr856'
Merge branch 'pr858'
Merge branch 'pr798'
Group chat button at the bottom of contact list resized to 16x16 like other buttons
Merge branch 'pr861'
Fix some nullptr dereferences in Audio

Fixes #859
Italian translation: update