WIP: Flash is now a ES6 module

What does this MR do?

Refactors our Flash module to an ES6 module that can be imported directly where it is required rather than relying on a global variable. There is still a global variable so that we can easily spy on it in our tests, but this can be removed once we have a way to spy on modules.

Also refactored it to not be dependant on jQuery, should get a tiny bit of extra performance from it & there isn't anything in this module that requires jQuery.