Currently, only Apertis version `v2021pre` is supported by this demo. In
order to make it easier to compile the runtime and app for another
version, only template files are now present in this repo.

The `generate-files.sh` shell script has been added in order to generate
the suite and application manifest for any Apertis version, without the
need to modify existing files.

This commit also adds a .gitignore file in order to ensure generated
files aren't pushed to the repo.

Signed-off-by: Arnaud Ferraris <arnaud.ferraris@collabora.com>