Add Postgraphile subscription exposure

- Add automation for TypeScript project build and tests via
  Webpack, tsc, and Jasmine
- Add custom Express application to serve Postgraphile
  subscription endpoints
- Add automated test suite for subscription endpoints

.gitignore

@@ -1,4 +1,5 @@
 .idea
+.vscode
 test_data_dir/
 contracts/*
 environments/*.toml
@@ -7,3 +8,6 @@ vagrant*.sh
 .vagrant
 test_scripts/
 vulcanizedb
+postgraphile/build/
+postgraphile/node_modules/
+postgraphile/package-lock.json