Fix IDE-1489

Updated shouldConfigure method for configuring Liferay nature in cases of no liferay maven plugin but the project contains liferay specific metadata files
This is a good approach but I would like to make things a bit stronger, so instead of just checking for existence of files, lets also make sure that liferay*xml files are located in the webapp docroot.  

Note that we can't just check src/main/webapp as some maven users may customize the war plugin to change this location.  See in the m2e-wtp (which we have as a dependency) there is a WarPlugin configuration object that you can use to check the folder value.