Scripting: Update Rockblock and MAVLinkHL scripts

[stephendade]

Updating the RockBlock and MAVLinkHL scripts to take advantage of the new gcs:run_command_int command.

Also added the gcs:run_command_long lua binding

Trying to debug the merge commits this time....

[stephendade]

Having trouble with git here ... I can't find any merge commits in my tree, so not sure why Github thinks there is a merge commit in here.

Sigh .... will leave this for tomorrow.

[stephendade]

A few changes here:

• The COMMAND_LONG to COMMAND_INT conversion now takes place in lua, using the conversion code in convert_COMMAND_LONG_to_COMMAND_INT() in libraries/GCS_MAVLink/GCS_Common.cpp
• I've added a GCS timeout option, where if it's been >5 seconds since a packet (heartbeat?) from a GCS, MAV_CMD_CONTROL_HIGH_LATENCY will automatically be enabled. So if the main telemetry link is lost, the High Latency link will automatically start (and vice-versa)

@peterbarker and @IamPete1 - not fussed as to whether we do the command_long -> command_int conversion in C or Lua. The Lua version's not too bad.