jetpack changed its xpi model
After some changes to the XPI model of AddonSDK, we cannot rely on package.json anymore.
You can get an example XPI by going to https://builder.addons.mozilla.org/addon/1000229/latest/ and clicking Download
We should read the required metadata (jetpackID, fullName, version?) from it and then combine the path to the directory that we will be scanning for entities basing on that (resources/JetpackID-name-lib/).