Fix bug in identifying master speaker IPv4 address

Fixes #1

Improve responsiveness to device changes

Process Push notifications when received from the device, to improve responsiveness to changes. Volume changes are now noticed immediately rather than having to wait for a polling interval. This allows reliable use with a linked hardware volume control.

More robust handling of communication failures

Some improvements made to handling of edge conditions while the speakers are booting or become unreachable.

V0.0.2

Initial release for installation through HACS