Add a new Python module called "updater", which contains the logic for
prompting the user to enable updates, and checking our GitHub releases
for new updates.
This class has some light dependency to Qt functionality, since it needs
to:
* Show a prompt to the user,
* Run update checks asynchronously in a Qt thread,
* Provide the main window with the result of the update check
Refs #189
Allow creating an RPM package that is to be installed specifically on
Qubes. This package has the following extra properties from our regular
RPM packages:
1. Make `python3-magic`, `libreoffice` and `tesseract` requirements
for installing Dangerzone, since the conversion takes place in a
disposable qube that needs these packages.
2. Ignore the container.tar.gz file, if it exists.
3. Add our RPC calls under `/etc/qubes-rpc`