Undeprecate Packet.getExtension(String)

as there a valid uses for it, see for example ChatStateManager:173.
Use ServiceDiscoveryManager.supportsFeature() in AMPManager
Remove unnecessary multiplication in DiscoverInfo.hashCode()
Rework DiscoverInfo

Make Feature and Identity immutable and allow fast lookup of those two
in DiscoverInfo.
Move is(Connected|Authenticated) and getUser()

into AbstractXMPPConnection.

Also remove wasAuthenticated field from XMPPBOSHConnection, it is
already in AbstractXMPPConnection.
Add IntelliJ and Mac OS X files to gitignore
Remove ServiceDiscoveryManager.getFeaturesList()

The method was redundant, getFeatures() did already return a copy of the
features. There is also no need to make it an unmodifiable List.
Require jxmpp 0.4.0
Fix javadoc warnings and deprecated methods
Smack 4.1.0-alpha5
Smack 4.1.0-alpha6-SNAPSHOT