Add "Initial value" field to Memory modules

[griffi-gh]

Needs compatability testing, extra properties SHOULD be zero-inited for existing levels... (set_num_properties clears)
existing levels seem to work just fine... but a check may still be needed

[rollerozxa]

What's the usefulness of this? Isn't it already possible to initialise a memory module's value with some circuiting

[griffi-gh]

What's the usefulness of this? Isn't it already possible to initialise a memory module's value with some circuiting

mostly just convinience + makes stuff like pre-inited RAM modules easier to build

[griffi-gh]

also, circuits have a 1 cycle delay