How to deal with quotes in javascript

@incuna/frontend 

Moved this to it's own issue so it didn't block the main JS style guide. 
The main decision here is that when the string content contains single quotes, should we:

* Always use single quotes and escape apostrophes (more consistent and a simpler rule) `var a = 'Hello, here\'s an apostrophe example';`

or

* Allow the use of double quotes if necessary to avoid escaping (more readable) `var a = "Hello, here's an apostrophe example";`

Attached is the original PR which implemented the latter, but I'm leaning towards the former now for consistency.