Create Fedora toolbox image based on current host machine version #1

This pull does three things, in order:

1. Retrieves $VERSION_ID from /etc/os-release.
2. Asserts that the $VERSION_ID matches the Fedora versioning pattern, to assure we are pulling a valid Fedora image version.
3. Finally, uses this $VERSION_ID to create the envision container with the appropriate Fedora image version.

This should resolve issues with version mismatches, such as the recent x264 conflict, and ensure compatibility with future Fedora versions. This should address issue #13.