What browsers are we targeting?

[Ambyjkl]

We have some ES6 code client-side, which means we would break on IE 11 among other browsers. I also see a bunch of vendor prefixes thrown around without much reason (including -ms ones for IE and -khtml for konqueror which would die due to ES6 anyway). Ways to tackle this:

• Come up with a "browserslist" (http://browserl.ist/) for the versions of browsers we are willing to target.
• Set up babel and postcss to do the transpiling and vendor-prefixes for us rather than doing it by ourselves

[nikolaevra]

I think google analytics gives us a good insight into that, Mainly chrome and Safari