Support more than one PCF version

[mattysweeps]

Wait until #34 is finished before starting on this.

Currently the PCF version (and various tile versions) are kept in the code. As committers update the tiles, the old versions are not really supported.

To do this we should:

• make a new flag for generate-config which allows for the specification of a PCF version. (default to latest supported version)
• Update CI infrastructure such that there is a pipeline for small runtime and large runtime PCF for each supported PCF version.