replacing the wasmer runtime with a wasmi runtime running inside an SGX enclave

[reuvenpo]

EDIT: This is still a WIP.

This PR includes the following pieces to it, from top to bottom:

• Patch go-cosmwasm to use local dependencies
• Copy cosmwasm-vm to a new directory containing the new wasmi+sgx code
• Adjust cosmwasm-sgx-vm to call the enclave (wasmi-runtime) instead of using wasmer Changes to sgx vm #129
• Define the interface between cosmwasm-sgx-vm and the wasmi-runtime
  • The types in this interface are defined in cosmwasm/lib/enclave-ffi-types and have autogenerated C bindings. See the .edl file in cosmwasm/lib/wasmi-runtime to see how they are used.
• Implement safe wrappers around the FFI on the cosmwasm-sgx-vm side
• Write the .edl file describing the interface between the enclave and the outside world
• Implement safe wrappers around the FFI on the wasmi-runtime side
• Use wasmi to execute the wasm contracts in the environment they expect, as defined in cosmwasm Wasmi enclave #123