Upgrade path and migration of database to fix issue #121 for affected users

[joshirio]

See issue #121

Currently all users who are using duplicated collections have many records in the database file with the sql table column _id set to NULL this causes issues when exporting and printing, ie. no records are retrieved.

Since the original issue has been fixed, we need a migration plan for users that have databases affected by this inconsistency. The solution would be to include an upgrade path with the 2.6 release that automatically upgrade the database on first start-up.

If implemented all users will have consistent data sets again after installing the 2.6 release.

Technical note:
SQLite doesn't allow editing tables directly so an approach would be to create temporary copies of affected tables and to recreate them properly with PRIMRARY KEY constraints, see https://www.sqlite.org/faq.html#q11