Simplify roster handling code

Merge result handling code into IqParser

Conflicts:
	src/main/java/eu/siacs/conversations/parser/IqParser.java
	src/main/java/eu/siacs/conversations/services/XmppConnectionService.java

Refactor IQ parsing and verify roster pushes

Fixes #20

Conflicts:
	src/main/java/eu/siacs/conversations/parser/IqParser.java
	src/main/java/eu/siacs/conversations/services/XmppConnectionService.java