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