New context struct

[hardyjosh]

Motivation

For #1100

Solution

Created a new Context struct that currently can optionally contain an Order. This could be extended in the future.

It then has fns to interpolate strings, looking for the vars and following the path. Currently supports order tokens (symbols, addresses, etc).

Added a context arg to the yaml parsing straits, then setup:

• When a deployment is being parsed, the order will be parsed first then passed to the scenario parsing fn (so bindings can be interpolated
• When a gui deployment is being parsed, the deployment's order will be used for interpolating field names and descriptions.

This won't work in practice yet, because we're still adding the new yaml handling to Gui and getting calldata's for Gui.

Checks

By submitting this for review, I'm confirming I've done the following:

• made this PR as small as possible
• unit-tested any new functionality
• linked any relevant issues or PRs
• included screenshots (if this involves a front-end change)