Javadoc fixes

- Add hint to reconnection configuration
- s/connection.getChatManager/ChatManager.getInstanceFor(connection)
- typos
Bump jbosh to 0.8.0
Provide a MUC method to create *or* join a room

MulitUserChat.create() will throw an SmackException if the MUC service
does not return a 201 status when entering a room. Some MUC
implementations don't return the 201 status but instead behave like
the room already existed.

If the user doesn't care about the room beeing locked until the
initial configuration has been send, he can now use the new
MutliUserChat.createOrJoin(String) method.

Also remove some duplicate code by creating the private enter() method.

Fixes SMACK-557
Move gradle signing code out of allprojects

because it caused asking for the key passphrase multiple times, i.e. for
every subproject.
Make gradle use the local maven cache
Change keyringfile example to real file

I'm always using the file and forget to s/foo/flo/
Smack 4.0.0-rc1
Smack 4.0.0-rc1-SNAPSHOT