testExecutionManagerPerformance threshold to 7500ms from 2500ms

- For BasicTaskExeuctionTest.testExecutionManagerPerformance
- Saw 5601ms on buildhive
extract perf tests from BasicTaskExecutionTest

- created BasicTaskExecutionPerformanceTest
- convert that to Java so no overhead/jitter caused by groovy code
Adds StartableMethods.stopSequentially

- And ControlledDynamicWebAllCluster uses it to stop everything, 
  even if stopping the control fails (i.e. continue with cluster next).
Merge pull request #803 from aledsage/fix/BasicTaskExecutionTest-timesensitive

Fix/basic task execution test timesensitive
Move ApiError class from rest-swagger to rest project.
TypeCoercions throws ClassCoercionException

Rather than ClassCastException. DefaultExceptionMapper in rest project
treats coercion exceptions as bad requests and other cast exceptions as
server errors.
Add optional 'details' field to ApiError

* Serialised as empty string if missing
* Added builder for constructing ApiError instances, with static
  fromThrowable(Throwable) helper
* DefaultExceptionMapper logs throwables at trace.
Merge pull request #814 from sjcorbett/rest-errors

Rest errors
Merge pull request #812 from aledsage/fix/ControlledDynamicWebAppClusterImpl-stopsAllEvenIfControllerFails

Adds StartableMethods.stopSequentially
fix brooklyn version
if brooklyn.war does not exist, start the REST API anyway,
and support a "dev mode" which allows it to load the jsgui if brooklyn.war is not found on classpath
(workaround for eclipse not copying the war to the classpath)
add abiquo, and support VM name maximum being configurable
fix logback version conflict in eclipse
fix bug where tree view refresh icon didn't re-render the refreshed collection (so tree didn't update)