Bug 617: Remove extend files from sal-rest-connector

Converted ControllerContext and BrokerFacade xtend code to java.

Addressed review comments:
  - Removed SupressWarnings "all"
  - Converted use of xext classes to guava
  - Removed sneakyThrow

Patch set 4: mistake - no changes

Patch set 5: Converted RestconfImpl

Patch set 6: removed xtend plugin anf dependencies from pom file

Change-Id: I45c22b22fee07a178faba9fcb9e52d3ff12a6697
Signed-off-by: tpantelis <tpanteli@brocade.com>