Add "copy" compilation mode into contract compilation process

[cpubot]

We have new contracts incoming which will be in the form of "raw Michelson". Simply putting those in packages/minter-contracts/bin is not sufficient, as that directory is often cleared out during the compilation process.

Create a new directory to house the set of "raw Michelson" contracts. During the compilation process (alongside LIGO compilation), these contracts should be copied into the packages/minter-contracts/bin directory such that

1. The subsequent type-generation process will pick them up, and
2. ./bin can be safely blown away and properly regenerated during compilation.

[cpubot]

cc @michaeljklein