Convert the check script to a script that sets the version to match
whatever Riot is being packaged.
Add a README because the two ways of interacting with versions are
starting to get complex to reason about.
Also add a docker build script.
* Replace the windows signing script with certificateSubjectName
option which finds the right certificate from the smart card
* Remove the windows signing script as electron-builder does it
out-of-the-box on windows
* Remove the cert file which isn't necessary with native signing
None of this will work as it will need tweaking (at the very least
I've not copied the origin migrator because that's had long enough)
but these are files which already existed in their current state and
so don't need re-reviewing.
