Add i18n functionality

[levimykel]

This PR adds the i18n functionality to this kit. It includes the following changes:

• Adds the lang and alternate_language objects to the document object
• Includes the definition of the lang query function
• Adds a lang wildcard value to the preview query function as well as the query helper functions that return unique documents (get_by_id, get_by_ids, get_by_uid)
• Adds a lang value to document links
• Updates and adds Kit tests for i18n