Add API to find services for a given feature

It's a common pattern to look for all services hosted under the users
service that provide a given feature. Let's provide an API for that and
use that API in the methods that benefit from it.
Make XMPPTCPConnection fail without a HostnameVerifier
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
Merge branch '4.0'

Conflicts:
	build.gradle
	smack-core/src/main/java/org/jivesoftware/smack/ConnectionConfiguration.java
	smack-tcp/src/main/java/org/jivesoftware/smack/tcp/XMPPTCPConnection.java
Merge branch 'master' into sasl

Conflicts:
	build.gradle
smack-java7 must depend on smack-sasl-javax
Allow null as return value of initialize()
Use sorted list instead of priorityQueue