[buteo-sync-plugins] Improve functionality for importing contacts via Bl...

[blammit]

...uetooth

• Use a "bluetooth" syncTarget to allow the contacts backend to avoid clobbering existing local contacts with data from a bluetooth-imported contact.
• Save the MAC address of the Bluetooth device that sent the contact in the QContactOriginaMetadata of the contact so that if we import from the same device later, we know we can safely overwrite any existing details.
• Add ContactImport implementation to allow existing contacts to be updated. We can't just clobber existing contacts completely as per the previous implementation as this will cause user-applied links to disappear.
• Apply the "slow" sync mode if this is preferred by the profile. This allows the client to request all contacts from the other device even if the other device has not made any changes to their contacts. This is the behaviour we want for an import-style operation.

[chriadam]

Cool, LGTM