feat(models): make action a generic type

[valorkin]

This is not an actual PR, more like proposal for consideration Typesafe maniac like would be really grateful for strictly typed Action

TS v2.2+ introduces defaults for generic types so Action<T = any> means Action is generic, but it will be any if type not provided

What do you think?

TS proposal here: https://github.com/Microsoft/TypeScript/issues/2175

[valorkin]

This feature just landed in ts 2.3