Atomic Demo Implementation

[liangping]

We need to implement a demo, following the spec
https://github.com/liangping/ibc/tree/atomic-swap/spec/app/ics-100-atomic-swap

Tasks:

• Create .proto file according the definitions in ics-100-atomic-swap.
• Generate go files from proto using buf
• Implement IBC Atomic Swap module and unit tests
• Using ibctest for module functional tests
• Integrate Atomic module to Simapp
• make a docker image for ibctest e2e test and upload to github.
• done e2e test.

Here is main task to do that. we can create separate issue for each of these tasks.