0.3

Support heterogenous simnets

• Add bitcoind
• Add c-lightning support
• Run on regtest instead of simnet
• Other improvements

Notable commits

c5c7130 change default SIMVERSE_DOCKER_IMAGE_PREFIX to "simverse/"
30da138 make simverse run on regtest as a prep for heterogenous simnets
4c74ac0 add support for bitcoind
4efa053 split base/builder images into base/buildtime/runtime images
3e922f9 add support for c-lightning

All new work: v0.2...v0.3