Duplicate virtual environments in CircleCI

[m3ller]

Application Currently, CircleCI builds and caches a virtual environment for each demo. This is wasteful especially if many of the demos share the same requirements.txt (i.e. they can run in the same virtual environment). As the number of demos increases, this will become a problem.

Proposed Solution Before building a new environment for a demo, check if it can run in an existing environment.

[m3ller]

Will wait for more demos to come in (and see their requirements) before deciding on how to implement a solution to this.