Creator automatically joins the group after creating it

...ndroid/src/org/briarproject/android/AndroidComponent.java

...ndroid/privategroup/conversation/GroupControllerImpl.java

...roid/privategroup/creation/CreateGroupControllerImpl.java

...iarproject/android/threaded/ThreadListControllerImpl.java

...rg/briarproject/api/privategroup/PrivateGroupManager.java

briar-core/src/org/briarproject/privategroup/Constants.java

...rg/briarproject/privategroup/PrivateGroupManagerImpl.java