Py-ioticagent

- Add property manipulation methods
- Ensure Python 3.8 compatibility, add to classifiers list
- Remove deprecated local parameter for search/describe

- Relax tag restrictions (in line with QAPI update)

- Relax tag restrictions (in line with QAPI update)
- Add extras_require for py-lz4framed

- Fix pending subscription timeout behaviour

- Fix thing re-creation handling when no agent assigned
- Remove unused acksecs parameter from AmqpLink

- Increase metadata tag length limit from 16 to 64
- Reduce incoming-data-without-callback warning logging level
- Calling agent methods when client offline now raises LinkShutdownException
instead of RuntimeError
- Log recurring connection errors only once (until reconnection success)
- Exit ThingRunner during retry delay rather than attempting step again
- ThingRunner stop() method returns True on succesful thread termination
- Let Control.tell (sync version) time out based on request-specific timeout
rather than agent-wide sync_request_timeout