Add sniff to ensure plugin prefix in deprecated_functions

[andizer]

When we deprecate a method, function or hook we use the build in WordPress functions for it. One of the arguments these functions should receive the version number and that's the location where different kind of forms are use. We should have a sniff that checks if the plugin prefix is in there as well as the version number. Just to prevent this: _deprecated_function( __METHOD__, '11.0');

We want: _deprecated_function( __METHOD__, 'WPSEO 11.0');