12 improve overlay

[wkmeijer]

• Refactoring of loads of things
• Add last send message + got last response message
• Implemented heartbeat timer, introduction request is send to 10 random peers every 5 seconds (#21)
• Identify peers by public key instead of username (#18)
• Network operator is no longer send along in messages (#24)
• Split overviewconnectionsactivity into two classes (#20)
• Fix minor bug with No Connection snackbar (#23)
• Fix dead overlay on restart (#8)
• add version number
• Documentation update (connection.rst)

A thorough test is needed to see if overlay really works flawlessly now. Furthermore backwards compatibility should be tested.