LPS-43148 Fix misspell in lang message
LPS-43148 Move frequently used import "FileExtensionException" to common/init - no logic change
LPS-43148 Update exception-handling in UploadImageAction

Similar pattern can be found in the EditFileEntryAction#handleUploadException, however, we should not add any error messages to SessionErrors when the action is "ADD_TEMP", as it is generated by a file-upload, not a full form submit. If we added the exceptions to both JSON and the SessionErrors, the user could get unexpected UI errors - coming from a previous action -, upon closing (hiding) and reopening the Logo Edito pop-up.
LPS-43148 Fix possible NPE in UploadImageAction

Steps to reproduce:
1- Open Logo Editor
2- Click on 'Save'
--> NPE occurs in the log, 'Portlet temporary unavailable' message appears on the UI
LPS-43148 Add form-validator to the file input field in image_uploader (view + logo_editor.js)
LPS-43148 Logo Editor generates FileExtensionException, even if the user uploads a file with an extension allowed
LPS-43148 Do not cache Logo Editor window
LPS-44148 Autofocus on the file input field in POP-UP window state as well
LPS-43148 SF - follow pattern from EditFileEntryAction (no logic changes)
LPS-43148 SF - we only need the name of the file (in order to keep the original extension)
LPS-43148 SF - missing namespace
LPS-43148 SF - avoid issue with the cleaned parameters
LPS-43148 SF - move variables to where they are used
LPS-43148 Sort
LPS-43148 Lang keys
LPS-43148 Sort
LPS-43148 SF