Improve the usability of ibc-testkit at a remote crate

[rnbguy]

Improvement Summary

Recently, it has been reported at #1257 that ibc-testkit in its current form is unusable at remote crate. I am listing the features that need to be added to allow ibc-rs users to leverage our testing framework easily.

Proposal

• Remove the dependency of AnyClientState - remote crate may have a different AnyClientState implemented - possibly with their own light client.
• Remove the dependency of MockStore or InMemoryStore - remote crate may want to use their own storage for integration tests.
• Remove the dependency of MockIbcStore - remote crate may want to use their own implementation of ValidationContext and ExecutionContext for integration tests.

Let's use this issue to track the progress on this. We will probably come across more.