A big number of improvements

First of all, whole range of existing features and using patterns have been remained unchanged. This means whole new functionality keeps invisible (almost completely) until user activates it.

**ChangeLog**
* Second language subtitles. File should be named as video_file_2.srt and could be activated with [ctrl+backspace] key. Second language subtitles available in all modes. Script keeps working fine without it.
* First and second subtitles could be shown on screen simultaneously
* Ability to add global time shift for subtitles and audio synchronization
* Ability to add any number previous/next phrases before/after current in Add Word dialog
* [R] key switches "always show subtitles" toggle
* Bug fixed: Sometimes there was subtitles duplication on screen