Make test slim by reducing sample data
Remove needress destroy_all
Convert Item's default_limit and remaining scope to lambda expression

Because the value of limit and offset are changed in spec test.

This error has been found by rspec --seed 38304
Refactor Item model using remaining and default_limit scope definition
Fix some specs to check of the filter by name

Fix the errors of rspec --seed 38304
Fix the specs for filtering by tag in entries#index

Fix the errors of rspec --seed 38304