Do explicit disconnect from server in some cases
Move wait for reconnect out from exception handler

This way the sockets and other objects created in main() can be released
before sleeping (otherwise they would remain active due to being included
in the frame kept by the exception handler)
Use a new TelldusCore instance to avoid creating cyclic references

Needed as report_devices is used in a callback registered with TelldusCore
No need to reset callback_dispatcher as of tellcore-py 1.1.0
Run travis tests on 3.4 and pypy3 as well
Require tellcore-py >= 1.1.0