Added /clean command to clear a user's additions from a channel

Any user with playlistdelete permission can now use the /clean
command to wipe out a user's additions to the playlist.  This
can be helpful for taking down abusive items en masse without
resetting the entire playlist.

The code should probably be generalized, somehow, to handle
title patterns or additions within a certain timeframe.
made slightly more efficient in response to comments
Added /cleantitle, and -i option to ignore case.

Fix #257, you should be able to clear username and title patterns
now with ease.  For best results, wait until they've wasted a lot
of time adding a lot of videos before you wipe them.
Added online help for /clean and /cleantitle
Removed help.html since it's not used anymore.
Added /clean command to clear a user's additions from a channel

Any user with playlistdelete permission can now use the /clean
command to wipe out a user's additions to the playlist.  This
can be helpful for taking down abusive items en masse without
resetting the entire playlist.

The code should probably be generalized, somehow, to handle
title patterns or additions within a certain timeframe.
made slightly more efficient in response to comments
Added /cleantitle, and -i option to ignore case.

Fix #257, you should be able to clear username and title patterns
now with ease.  For best results, wait until they've wasted a lot
of time adding a lot of videos before you wipe them.
Added online help for /clean and /cleantitle
Removed help.html since it's not used anymore.
Merge branch 'master' of https://github.com/unbibium/sync
Merge pull request #281 from unbibium/master

[MERGE] Add /clean and /cleantitle commands for moderators