Add more detailed development documentation

[latenitefilms]

I'm just going to use this issue to jot down personal notes about how the OpenFX plugin works, so that I can eventually update the Gyroflow Documentation with some more detailed developer notes to help others make Gyroflow plugins.

instance_id

yes, it's a random ID I save in a openfx property (hidden string field)
the idea is that when user copies the effect, that id will remain the same
or cuts the clip
then we don't have to create a new instance, surface and memory
but when user modifies any settings manually or reloads project, that instance id is generated again
also, it's for the use case, where you have a clip with the effect, you cut or copy it multiple times, and you change only one instance, but you want the rest to remain intact