Implemented Paste Over Text

[eltomito]

This implements a version of Paste that overwrites the text with clipboard contents while leaving time codes unchanged.

This command is super useful, because it's the only way you can turn two separate srt files into one subtitleeditor project where one of the original files becomes the text and the other one becomes the translation.

It is also useful when somebody translates the text of the subtitles in some other program and you have to insert it back into the timed subtitles.

[felagund]

I have a Python script that does this (it basically takes timing from one subtitle file and text from another and combines them), would be usper useful to have this in the program itself.