Fixed UF-67 by making JGitFileSystemProvider not a singleton

This fix uncovered a pre-existing issue with AbstractIOService.startBatch() which is now
documented as UF-70.
Fixed a (recently introduced) XSS vulnerability in the login page
Followed through on the ability to configure a JGitFileSystemProvider without changing system properties
Switch to lighter-weight encoder dependency (no transitive deps)
Updated tutorial doc to work with the latest stuff
Finished documenting annotation processor setup
Factored out copy-n-paste code from the implementations of WorkbenchPanelPresenter
Fixed UF-46: Methods of WorkbenchPanelPresenter that take PartDefinition args should return boolean

This fix had a ripple-down effect on the underlying APIs that actually perform the operations that
could silently fail.

I also had to modify a test assertion due to the tighter contract on what it means to "remove" a view
from a panel that can only hold one thing at a time.
Fixed the ordering of steps to clear APT problems
Fixed UF-75 and UF-77: annotated methods that break the rules are now flagged as errors

Previously, the methods were silently ignored at code generation (javac/IDE compile) time.
Fixed UF-78: Resource leak in AbstractMultiPartWorkbenchPanelPresenter (was BaseMultiPartWorkbenchPanelPresenter)

The mocking in these tests is a bit over-the-top. It would be nice to clean it up some time.

Also, the tests don't cover all possible context resolution permutations. There are a lot of them. The tests mostly
focus on the code paths that ensure the resource leak test is doing something valid.
Fixed warning/error checkers so they work correctly in JDK6 and JDK7.

Problems still remain under JDK8, but there are also other UF modules that don't
build correctly under JDK8.
Fixed UF-81: uberfire-tutorial does not compile due to missing weld-api dependency version
Fixed UF-45: Simplify uberfire-client-webapp setup

No need for fancy jetty+ stuff when deploying client-only functionality
Fixed UF-80: Remove leftover unused security types
Improved API docs by explaining the Activity concept and ActivityManager operations.
Further cleanup of Activity-related javadoc
Fixed typo in previous commit. Sorry about that!
Switching to the official PicketLink filter rather than the temporary one bundled in Errai snapshots
Initial implementation of User Management screen