Add API module

opentech/static_src/src/app/src/api/index.js

opentech/static_src/src/app/src/api/submissions.js

opentech/static_src/src/app/src/api/utils.js

...c/src/app/src/components/SubmissionsByRoundListHeading.js

...src/src/app/src/containers/SubmissionsByRoundContainer.js

opentech/static_src/src/app/src/index.js

opentech/static_src/src/app/src/redux/actions/submissions.js

...tech/static_src/src/app/src/redux/reducers/submissions.js

...ech/static_src/src/app/src/redux/selectors/submissions.js

opentech/static_src/src/app/webpack.base.config.js