Make ProviderManager static

also remove initialize() from ProviderFileLoader, by simply putting the
code into the constructor.
Tell Gradle to download javadoc

when creating the classpath for eclipse.
Make IQ attributes final in parseIQ()
Add 'null' check to parseContentDepth

Does not fix the actual problem, but at least prevents resource
allocation until OOM.
Merge branch 'master' into osgi

Conflicts:
	smack-core/src/main/java/org/jivesoftware/smack/initializer/UrlProviderFileInitializer.java
Move OSGi Declarative Service definition in correct folder