Move ThreadedFileWriter class to libmythbase

No change of code or functionality
Update ABI version
Add local file support to RemoteFile class

RemoteFile was only able to open remote, non-local files. This adds convenience so you don't need to know what type of files you're dealing with to access them.
In write mode, use a ThreadedFileWriter, in read-only mode use a QFile
Update ABI following update to RemoteFile class
Fix leak in mythmetadatalookup

Don't want to use takeFirst() here as it would leave the MetadataLookup* object dangling.

Ref #11754
Update metadata artwork if current artwork point to invalid or non-existing data

Older version of mythtv could have used local path as metadata artwork, making them non available on remote frontends.
This prevent having to do "Reset Details" followed by "Retrieve Details"

Fixes #11764