The existing approach didn't expose when the download was complete.
By fetching the file upfront and downloading from a blob we can better
estimate when the download is complete because we load the file in
memory, and then download from there.
The promise resolves after the file is in memory, so the delay between
the promise resolving and the file actually being downloaded is a lot
shorter, and based on the size of the file.
closes https://github.com/TryGhost/Team/issues/2206
- removes `www.` from the url shown on links table in post analytics
- we had previously removed http(s) protocol from it as well, and they are only shown while editing the url
no issue
- pattern of downloading a file by creating an iframe and setting the `src` attribute was repeated throughout the codebase and was using a mix of native and jQuery patterns
- added a `utils` service for housing one-off utility methods like this to avoid repetition and mixed patterns becoming more widespread (we want to get rid of jQuery usage)
