Add mutator choice for web and cli

[vbvictor]

Add functionality to actually choose mutators from web UI and CLI interface.

Also added support for files-filter to cli/generate_patches.py. Now it's just like in web version, where user can choose line_begin and line_end. I'm not sure if the format of files-filter in CLI is the best one. I would be happy to change format based on your comments.

In README, I added a table of all supported mutators so that users would not have to read source code for available mutator IDs to pass into cli/generate_patches.py.