[FEATURE] Optional base atom for Event Instancers

[mutmedia]

Is your feature request related to a problem? Please describe.
It's frustrating having to create/choose a base AtomEvent whenever using an EventInstancer, especially since most of the cases they are the same.

Describe the solution you'd like
I'd like to be able to not add any base events and it still work (I understand the rare usecase for base events)

Describe alternatives you've considered
The solutions I thought of were either removing the base event entirely, or making a null check and instantiating a new event of the required type at runtime

[AdamRamberg]

Thanks for this issue! This sounds good to me. Just use CreateInstance if _base is null. The one doing this change will also need to remove the assert on OnEnable. I will label this issue "ready to be developed", so whoever feels motivated could grab it and start develop it

[mutmedia]

There's a PR out for this (and #171)

[AdamRamberg]

Closed by #172