JBIDE-15428 - No JAX-RS problems when importing a project that contains HTTPMethod annotation without @Target and @Retention

Skipping the Java ElementChangeEvents when the Java Project is not open yet. This avoids race conditions during import.
Bonus: import seem to be twice as fast as before ;-)

Other changes:
- Move the call the JaxrsMetamodel#setBuildStatus() to finally{} blocks of JaxrsMetamodel#processXXX() methods
- Adjusted some javadoc, log messages and catch() blocks (avoiding to catch Exception or Throwable)
- Added a ReadWriteLock on all public methods of the JaxrsMetamodel to avoid concurrent access to the metamodel by different threads, for example if an async build
is still running and the validation is started. This avoids the following type of error:

{code}
!ENTRY org.jboss.tools.common 4 0 2013-10-09 18:17:54.307
!MESSAGE
!STACK 0
org.jboss.tools.common.validation.JBTValidationException
	at org.jboss.tools.common.validation.ValidatorManager.validateInJob(ValidatorManager.java:101)
	at org.eclipse.wst.validation.internal.operations.ValidatorJob.run(ValidatorJob.java:78)
	at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)
Caused by: java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
	at java.util.HashMap$ValueIterator.next(HashMap.java:822)
	at org.jboss.tools.ws.jaxrs.core.internal.metamodel.validation.JaxrsMetamodelValidator.validateAll(JaxrsMetamodelValidator.java:268)
	at org.jboss.tools.ws.jaxrs.core.internal.metamodel.validation.JaxrsMetamodelValidator.validate(JaxrsMetamodelValidator.java:153)
	at org.jboss.tools.common.validation.ValidatorManager.validate(ValidatorManager.java:117)
	at org.jboss.tools.common.validation.ValidatorManager.validateInJob(ValidatorManager.java:81)
	... 2 more
{code}

- added some tests to increase code coverage
JIBDE-12860 - JAX-RS validation problems are not linked

Fixed the problem where some markers would not be removed from the resource to be validated between
two validation calls, which meant that duplicate markers for the same problem would exist on each
resource.

Also refactored the search/element retrieval: the JaxrsElementIndexationDelegate now not only
deals with the Lucene indexation and searches, but also uses the metamodel to return List of
JAX-RS elements, Endpoints or workspace Resources.
Renamed some marker deletion/undexing methods to use the "remove" verb (eg: "removeMarker()") and be consistent with the
existing "remove()" methods that remove the elements themselves.
Added JUnit tests to covers the fixes.

This patch also fixes:
- JBIDE-15662: Warning Multiple JAX-RS Activators doesn't disappear
- JBIDE-15664: Application path configured in web.xml causes warning