webadmin,userportal: Use thread-based workers for GWT compilation

This patch ensures that thread-based permutation worker factory
(ThreadedPermutationWorkerFactory) is used for GWT compilation.

Instead of launching external workers as Java sub-processes
(CompilePermsServer) communicating with main GWT Java compiler
process via socket, this patch makes GWT Java compiler spawn
internal workers as threads. This should reduce overhead when
compiling lots of permutations.

gwt.jjs.maxThreads is set to 4, which means:

  max_worker_threads = min(localWorkers, 4)

where localWorkers is controlled by gwt.compiler.localWorkers

(For details, see ThreadedPermutationWorkerFactory line 84)

In practice, this patch means we can have up to 4 internal
(thread-based) workers active at the same time during GWT
compilation. The actual number of thread-based workers is
controlled via gwt.compiler.localWorkers option.

Change-Id: Iabdbe43ba186d4fde646b01fee3d5196ff35e8ba
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>