renamed UserAgent according to specification
Merge remote-tracking branch 'origin/master'

Conflicts:
	src/main/java/com/yandex/money/api/net/DefaultApiClient.java
Merge branch 'dev'
DefaultUserAgent class added
Merge remote-tracking branch 'origin/master'

Conflicts:
	src/main/java/com/yandex/money/api/net/DefaultUserAgent.java
Merge remote-tracking branch 'origin/master'
Updated OkHttp library and fixed P2pParams bug.
Added group method for convenience.
Added header Location.
A little bit of refactoring.
Fixed session request method when there are no POST parameters.
Extended Revoke method.