Insteon_Diags: Remove all Old References to Ping Timer

Get rid of old devcat type entries and related ping timer that is no longer used
Insteon_Diags: Restore Devcat Support, Add Support for Firmware

Reintroduced method to request devcat that was previously called ping and overwritten by a real ping command.  New method to request devcat is called get_devcat().

- Once devcat is obtained, it is saved through reboots and can be retreived with devcat() routine
- Now also saves firmware which can be retrieved with firmware() routine

We do not currently use the devcat values, but I could certainly see using it in the future.