Fixes#21533
Before we just assumed that the passed path was a file. This does not
have to be the case. Thus check if it actually is a file before doing
any more tests.
In case of an error the error message often contains sensitive data such as the full path which potentially leads to a full path disclosure.
Thus the error message should not directly get displayed to the user and instead be logged.
add colon to translated string
use placeholder in t()
Adding a size limitation for avatar upload
Unit test for file size
Fix typo & display server side error message
* Original avatarcontroller migrated to the appframework
* Added DataDisplayResponse that show data inline in the browser (used
to retrun the image)
* Removed some unneeded code
* Added unit tests for the avatarcontroller
