Removal of deprecated security components.

As almost all of them were unused since the switch to
Shiro Guice Support (ShiroModule that we extend).
Still, by the fact that many UTs were not setup properly,
many UTs did pull in those deprecated plexus components
instead performing tests with code we use at runtime.
These plexus components are now removed, and
SecurityModule properly installed, that involved
some UT class hierarchy changes too. NexusAppTestSupport
is now the class that should be extended when
security is needed to be present in UT.

Another problem was pollution of "main" thread
Shiro related threadLocals, as when one test performed
login, the whole Shiro object graph remained pinned
in memory (as delegating subject tied to main thread
referenced SecurityManager and other stuff). Hence,
some UTs were able and were testing against
SecurityManager started in some completely different
UTs (as all the tests are run in single JVM).
NexusAppTestSupport (and few other classes in some
non-core modules) modified now, to properly clean
the thread local state of main thread.
Class hierarchy change was wrong

As it caused to have Timeline inited well before
test prepared "legacy" content.

Removed redundant AbstractTimelineTest as the two
timeline UTs needs different environment anyway.
Merge remote-tracking branch 'origin/master' into remove-deprecated-security
Merge remote-tracking branch 'origin/master' into remove-deprecated-security
UT should cleanup after itself.
Merge pull request #46 from sonatype/remove-deprecated-security

Removal of deprecated security components.