Maintaining a wifi connection in manual mode with threading enabled

[indraastra]

@indraastra

1. Some method of detecting connection status and failures for user feedback / debugging - There's no Particle.connecting(), and cloud-related system events have not been fleshed out yet.
2. Full manual control of cloud connectivity - Issue #748 Once a connection is attempted, the system firmware takes over the reins and reconnects and resets as it sees fit.

Adding to the list above:

3. Nonblocking WiFi.connect() & Particle.connect() [ reference ] - There seems to be an issue where user code is blocked for a few seconds at a time even with SYSTEM_THREAD(ENABLED)