Improved "constant" handling

The latest Maia EAP release contains a few improvements regarding handling of configuration properties:

• plugin specific constants (currently Convention, OSGi, REST plugin): specific properties of these plugins are automatically added to autocompletion if the given plugin is present in project
  


• support handling in web.xml via <init-param> for Struts 2-Filter

Next will be automatic resolving of all current configuration properties, finally opening the door to long awaited features (amongst them builtin support for Convention plugin).