Fix photo editor

[tomasMizera]

Fixes multiple issues with the photo editor:

• show trash icon even when the image is not available (previously it showed the icon only when the Image was loaded successfully)
• update the text of the MMRemovePhotoDialog to better represent what it does
• photos were not removed from the project even if the Delete photo was selected. The issue was that the callback function onFormSaved was placed in the private QtObject and thus could not be called from the form
• we used to call root.editorValueChanged( "", false ) where the boolean value represents if the new value is null. We were passing false even when removing the photo. Changed it to true.

[github-actions]

Pull Request Test Coverage Report for Build 8661324422

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.03%) to 60.073%

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Files with Coverage Reduction	New Missed Lines	%
input/core/merginuserinfo.cpp	1	74.45%
input/app/projectsmodel.cpp	5	65.75%

Totals
Change from base Build 8651536739:	0.03%
Covered Lines:	7586
Relevant Lines:	12628

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💛 - Coveralls

[PeterPetrik]

shouldn't unlink photo button has grape border (as secondary button)?