Add functionality for disabling and enabling Ycm autocompletion.

This is the better solution for this pull request that i made this morning https://github.com/Valloric/YouCompleteMe/pull/1165

On that PR autocmd was triggering even when Lock command was called. In this PR that is fixed, so now when you call `YcmLock` it disables autocommands for CursorMoved and CursorMovedI.

Fixes #1164