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
BPMSPL-38: Asset Oracle: Cross-referencing (so asset editors know about other assets). Cherry-picked from 0924b3668b23db391987547aa4cac5ceaa1552f4