Use single threaded ExecutorService

for PacketListeners. Fixes SMACK-583.
Fix ExperimentalInitializer
Add SmackAndOsgiInitializer

OSGi ServiceComponents need the activate method, make sure it exists for
every SmackInitializer by using this class.
Add getDatestamp() to build.gradle
Smack 4.0.1
Smack 4.0.2-SNAPSHOT
Add support for HostnameVerifier

SMACK-586

Conflicts:
	smack-core/src/main/java/org/jivesoftware/smack/ConnectionConfiguration.java
	smack-tcp/src/main/java/org/jivesoftware/smack/tcp/XMPPTCPConnection.java
Fix OSGi component definition for smack-resolver-javax

The Service Component definition for resolver-javax is in
org.jivesofware.samck and not org.jivesoftware.smack*x*.

SMACK-576
Smack 4.0.2
Add support for additional attributes in the Message packet for Smack 4.0.x