Change 'brew_tag' to 'product'

One must run the command `rake db:migrate` to upgrade the database ett

- Renamed table 'brew_tags' to 'products'
- Renamed column 'brew_tag_id' to 'product_id' in the relevant tables

- Renamed views that were using BrewTag to Product
- Renamed variable names named 'brew_tag' to 'product'

- Refactored the manual_log_entries views so that they stop referring to the
  columns 'from' and 'to', but instead to 'start_time' and 'end_time'

- Deleted attributes test -- not used anymore
- Refactored some of the fixtures used in test so that the tests will start
  passing again