sellSideStrategy should use fewer operations in the case where an inside offer is canceled

[nikhilsaraf]

Desired Behavior

I want to be able to cancel some inside offers in my level provider without having the bot modify all the offers and cancel the last offer. The bot should just cancel the inside offers.

Impact

The desired behavior will lower my fee when submitting transactions since it will have fewer operations.

Feature Suggestion

We can achieve the desired behavior by augmenting the state transition logic in sellSideStrategy that converts levels to operations.

Additional Context

This is a follow-up to #46