UBports Installer 0.4.17-beta

A snap package is available by running snap install ubports-installer on any Linux distribution.

A small maintenance release fixing a sandboxing issue that affected all Linux packages. This also removes the requirement for double-dashes for command-line arguments, i.e. the Installer can now be invoked with ubports-installer -h rather than ubports-installer -- -h. Additionally, the update links have been fixed and now always point to the right package.