Add Revenant UBM-1A to data

[Sleet01]

This was based on the 2R file, but modified:

• removed 1 ton of armor
• removed small cockpit
• removed Remote Drone Control System
• removed two IS ER Medium Lasers
• removed two half-ton LMG ammo
• added regular cockpit
• added Smart Robotic Control System
• added two IS Medium Pulse Lasers
• added one ton of LMG ammo in CT
• modified Model, MUL ID, Era, and source

New mek loads fine and is usable by Princess.
Note: the expected BV is 784, PV is 25. MegaMek produces nearly these values (785 / 25), which may be due to incorrectly rounding the raw BV of 784.7 naturally, but I'm not sure.

Close #4855

[HammerGS]

Thanks!