Add support for installing PiritaFiles
This PR enables support of PiritaFiles with the USE_PIRITA=1 flag, which will force the CLI
to install the packages in the PiritaFile format (and convert them if backend support isn't there yet).
After conversion, a command is created in the /wapm_packages/.bin/command to help with
auto-completion later on.
Fixes https://github.com/wasmerio/pirita/issues/17
@syrusakbary you can review the PR now
@syrusakbary ready for review + merge
@syrusakbary only linux-aarch64 is not passing, we wanted to transfer this to wapm-cli-private
Tests will be green again after #266 will be merged.