Provide default props file for use by mods

Topics Props:
- BT libs vs injectors (vs netstandard2.0 libs)?
- provide variants: ModTekBattleTechMod.props, ModTekInjector.props(, ModTekNetStandard.props)
- or: ModTemplate.props, InjectorTemplate.props
- (dont repeat modtek, template name good if too much in props)
- ModTek provided: HarmonyX, Mono.Cecil
- Does not matter what the mod wants, its the mod pack that decides the actual version anyway
- Compile time only: Kraf.Publicizer and PolySharp, LangVersion
- Might hurt to pre-set in case a mod is using newer than installed BTA/RT
- Maybe version them? Like ModTekCSharp13.props