Add out-of-mech combat page

[infinitymdm]

• Add a page describing the Advantage point system for out-of-mech combat as in Add some simple "Out of Mech" play rules #56
• Address minimal mech vs. non-mech combat stuff as in Add rules for how mechs interact with out-of-mech combatants #57
• Also fix sticky discord banner to bottom of page by adding a fill-spacer to the template

[infinitymdm]

@Icosahunter We briefly discussed some small issues with this. Could you remind me what the concerns were?

[Icosahunter]

I kind of wanted to discuss the system and see if there are any changes we want to make based on discussion in the Discord etc. But on second look I think it seems pretty decent, good enough for testing in Beta. There are a couple typos, "atack" in the 2nd to last paragraph and "come" should be "comes" in the last paragraph. Fix those and then go ahead and merge it.