Automate PLMN swapping

[axis7818]

Currently, swapping PLMNs requires a telnet session to run the following commands:

• cellid [MCC] [MNC] to setup the new PLMN
• reloadPLMN to apply the change

This should be enabled through the sar javascript SDK.

[axis7818]

added a function call to the sar object in javascript. sar.changePLMN('310', '410');

It is not currently called. I could see building several default schemes for swapping PLMNs.

• stay on one value
• rotate between different of PLMN values
• etc.

[axis7818]

PLMN can be swapped from the flight controller