GitLab

The script will continue with the rest of the uploads but will exit with
a non-zero code so that we'll be notified to upload the missing files
manually.

We were running out of space in both of our github and gitlab
repositories due to storage limits. This change switches to using the
github REST API to upload torbrowser binaries as releases. Releases are
not subject to the space limits of repositories and, even better, do not
count against our bandwidth limits when users download them.