Added Byte-Order Mark check

Added check for all Byte-Order Marks documented on Wikipedia, although some of the marks like UTF-16 quite obviously render the site unusable by themselves.

Addresses issue #156
https://github.com/Automattic/vip-scanner/issues/156
Change slug in add_error call to use parameter value

Having the parameter value as the slug facilitates unit tests
Adjusted pattern match to avoid a parameter like livefyre3 being flagged thinking it was livefyre3

When I modified the code to accept parameters without quotes, I had missed the fact that the pattern would match when livefyre3 was used. Modified pattern to  specifically look for single quote, double quote, comma or space after parameter.
Added unit tests for new VIPParametersCheck class