Add idevicepairing tool to allow pair/unpair and listing existing pairings

Title describes it. During merge of the ipheth kernel module into the kernel a discussion came up to decide into which component of the stack pairing will take place. Since now, ipheth has had some extra support package which included a simple pairing utility and an udev rule to spawn it in order to set TrustedHostAttached to true in lockdownd effectively "enabling" the tethering USB interface to work with the ipheth kernel module.

As libimobiledevice does handle the pairing "private/internal", we require a simple tool to allow manual pairing, unpairing and listing of existing pairing records. This can then be used by the ipheth udev rule to auto-pair and set the required lockdown value.

Another thing to note here is that we initially wanted some kind of dialog in the desktop layer "Would you like to pair the device with this computer?" before actually starting any further communication (GVFS, ...). Might be time to revise how this fits into this workflow...