Code for adding 'Language' to the database

- Database changes (CatalogueDBAdapter)
- UI/XML changes to add 'Language' field (edit_book.xml,
book_details.xml & strings.xml)
- added to BookDetailsAbstract to ensure displayed/saved
- added to arrays in FieldVisibility.java
- shown or hidden in BookEditFragmentAbstract
Merge pull request #484 from Grunthos/master

Language field added