Add DB indexes

We should add some indexes to our database for these fields:

1. institution.current_password - expedite lookups by password
2. institution.institution_code - maybe also rename this to just code at this time
3. resource.resource_id - maybe also rename to code as above?
4. password.pasword - expedite lookups by password
5. institution_groups.code - expedite lookups by code

Update internationalization file (en.yml) accordingly with any renamed fields.