There is no more need for synchronization in listeners as they are all
executed in the same thread (aka thread safety via thread confinement). 

Listeners have been changed accordingly by: 
- removing thread safe data structures
- removing unnecessary synchronized blocks 
- removing WorkbenchJobs to run task in the UI thread. The concept of
infrastructure job disappears at the same time.

Change-Id: Ie4aa98b29c7272c22dccc3fcc84d29b78e7448bf
Signed-off-by: Mikael Barbero <mikael@eclipse.org>