Theme translation compare missing term corrected

- (Corrected) If translation file has same name with other translation
files some terms missing.
Add "watermark.png" to "$_UNUSED_IGNORED_FILES"

$_UNUSED_IGNORED_FILES
- Add watermark.png file
- Add true default no source image Settings::get('no_source_picture')
Element Detail Label Correction

@akaradeniz catch from community
Merge pull request #156 from trk/master

Theme translation compare missing term corrected