Add a toggle to write to keywords instead of plugin metadata.

[ayman]

Add a toggle to write to keywords instead of plugin metadata. Some people want keywords directly written. Allow this via a toggle.

[ayman]

I believe these lines can be updated with this call photo:addKeyword( keyword ) on the selected photo can do it. You'll need a LrKeyword object which you'll have to create with catalog:createKeyword( keywordName, synonyms, includeOnExport, parent, returnExisting ).

This should be made under the parent keyword textrso it can be filtered out or deleted easily.