Remove JS dependancy on Lo-Dash (underscore)

:warning: DO NOT MERGE YET :no_entry_sign: 

Handlebars.js is a requirement for SlotPicker. This PR swaps Lo-Dash for Handlebars for templates on the visitor details page to reduce JS dependancies.
It's incase the CDN isn't available for any reason, the resource is then loaded from our domain. For example, if the GSI network has not whitelisted cdnjs.com.