Rewrite ImperialConfig Angular Service

[sebastianbarry]

Child issue of #977

• js/config/imperial.js (has been mostly rewritten into useImperialConfig.ts anyway)

In looking at the 2 files:

• https://github.com/e-mission/e-mission-phone/blob/master/www/js/config/imperial.js
• https://github.com/e-mission/e-mission-phone/blob/master/www/js/config/useImperialConfig.ts
  I see that there is not much difference between the 2 files. My goal will be to get rid of imperial.js, and making sure that all functions that use imperial functions no longer rely on imperial.js and use useImperialConfig.ts

[JGreenlee]

Huh. Well I thought there were some functions that hadn't been rewritten yet, but I guess I already did that.
Once you've verified that imperial.js is not used anywhere, go ahead and remove it and we'll call it a day.

After that, maybe you can start to rewrite CommHelper from www/js/services.js?

[shankari]

Before we move on, we should also write tests for useImperialConfig.ts
I merged e-mission/e-mission-phone#1033 to master yesterday, so you should have a template to look at