Code cleanup. s/Lang/Language. Move some code from SDM to Packet and Discover(Info|Items)

Conflicts:
	source/org/jivesoftware/smackx/packet/DiscoverItems.java
Makefile: added javadoc target
PingManager: Fixed imports
SMACK-345: Improved detection of last activity. Properly synchronized access to lastMessageSent and registerd last activity namespace with ServiceDiscoveryManager. Improved LastActivity Provider