Updated subtitle_mark validations:

* updated run lists
* added 'is_primary_repo' config setting so that we can apply scripts to english only
* added 'relative_path_to_primary_repo' config setting so that foreign repos can load data from english
* removed Validation::SubtitleMarkChanges. This is now part of Validation::Content
* refactored validation code for consistency and readability
Updated subtitle_mark validations:

* removed standalone validation for SubtitleChanges
* load subtitle_marker csv files from primary repo (English)
* remove validations of PT files. They are currently not used
* refactored code for consistency
* updated rtfile
* skip if subtitle_markers CSV file doesn't exist