Enable custom title for ImageGroupDisplayable #558

[odifek]

Enable custom title for ImageGroupDisplayable #558

• Show a dialog after selecting and adding multiple images.
• The user can give the image group a title
• If no title is provided, the file names would be concatenated to form the image group name.
• Image group title is saved with the schedule.
• Handle backward compatibility of ImageGroup XML

The new structure of ImageGroup XML

<fileimagegroup>
<title>Image Group Title</title>
<files>file1;file2;</files>
</fileimagegroup>

• Remove unused LOGGER property

Please I will love some feedback on this implementation. Especially with regard to the dialog. Also concerning the dialog title and text, should the localization be done in a separate ticket or is it okay to do it here?

Feedback is appreciated. Thank you

[odifek]

I synced my fork with upstream. I am not sure why the other changes that are already on master are duplicated here