Replace Instance 'Context' with subclassing

[ColonelThirtyTwo]

See also: GmodStarfall/Starfall#139

The instance 'context' is a table of options for an instance, for example the ops limit. This was a carry-over design choice from E2 and does not work well with many options.

A more flexible approach would be to change settings by subclassing the instance and overriding the desired methods or values. This would also help libraries using SF to keep track of related data on an instance (ex. the processor 'entity')

[ColonelThirtyTwo]

Here's a simple OOP library that can be adapted for gmod: https://gist.github.com/ColonelThirtyTwo/7401493