Added random heavies/assaults, excess mechs go to storage

[Cydonia07]

• User can specify to start with a number of heavy or assault mechs - #1
• If user specifies a total number of mechs > 6 in the settings, the excess mechs go into storage.
• Read settings from an external settings.json.

[mpstark]

A couple things prevent me from merging this immediately.

• I don't want a separate settings.json
• I initially left out mechs that I felt were not a good fit for a random start, I'm unsure if I'd like to change this
• JSON doesn't support comments natively

It's fine if you don't want to fix these things, I can do them myself eventually, when I'm not working on something else.

[Cydonia07]

No problem; I'm just learning my way around the BT mod scene and saw that the settings.json method of loading mod settings is a common approach so I tried my hand at that. Should be a quick revert to remove that file from the repo and change back to the prior method of retrieving settings. I'll push an update shortly.