docker builder for building contracts

[ailisp]

#40 Also update all wasm to be built by this docker. By building on docker I found it's conflicting of rust-toolchain file and cargo +stable (error: stable is not installed). Since we want pinned toolchain, I think we should all stick with version in rust-toolchain file.

[ailisp]

We need also pin to a specific stable rust version to produce deterministic wasm output. We now pin rust-toolchain to nearcore's rust-toolchain, but that's a nightly and for use near-runtime-standalone in tests. Does latest (1.44.1) sounds good?

[ailisp]

@olonho a working contract builder image, might be helpful to you