BRP Resource methods

[mweatherley]

Objective

So far, built-in BRP methods allow users to interact with entities' components, but global resources have remained beyond its reach. The goal of this PR is to take the first steps in rectifying this shortfall.

Solution

Added five new default methods to BRP:

• bevy/get_resource: Gets the value of a resource with a given name.
• bevy/insert_resource: Serializes an input value to a given resource type and inserts it into the world.
• bevy/remove_resource: Removes the given resource from the world.
• bevy/mutate_resource: Replaces the value of a field in a given resource with the result of serializing a given input value.
• bevy/list_resources: Lists all resources in the type registry with an available ReflectResource.

Testing

Updates to the remote server example incoming.