break src into modules and improve testing

[tomwayson]

Expected behavior

• we can break esri-loader.ts into multiple files/modules (utils.ts) each w/ own test file that imports only the modules it needs to test
• we can use karma and it's watcher/plugins to run tests w/o having to use external watchers and bundlers
• tests can be written in TS

Actual behavior

• utils is included in esri-loader.ts
• the current test script uses an external watcher to run a production build and then karma each time a file changes
• tests are written in ES5

[tomwayson]

karma-typescript looks like it should do the job on the testing front.