Added webResourcesValidators extension point. fixes #14

This fixes #14 

Take a look at the adopter side of this extension point here: https://github.com/gamerson/liferay-ide/commit/b6503ad4e50b015c0f0d4b16b123a4246d914da1
Ok thinking about this again... if the name of the interface is "IgnoreValidator" then the primary use of this class is for ignoring so I think the method should be "shouldIgnore'? right?