This change updates the project structure to become flattened.
Previously, the simulator, frontend and API each lived into their own
directory.

With this change, all modules of the project live in the top-level
directory of the repository. This should improve discoverability of
modules of the project.

This change adds an initial set of benchmarks for the resource
consumption framework in order to measure the effect of changes on the
performance of the simulator.

This change adds a generic framework for modeling resource consumptions and
adapts opendc-simulator-compute to model machines and VMs on top of
this framework.

This framework anticipates the addition of additional resource types
such as memory, disk and network to the OpenDC codebase.