Allow users to disable mappings completely

`let g:editqf_no_mappings = 1` will prevent editqf from defining
mappings. Useful if a user wants no mappings or only wants one of them
(which can't be done with just hasmapto).

Also, adjust whitespace after bang to match rest of file.
Merge pull request #2 from pydave/add-nomappings

Allow users to disable mappings completely