Merge pull request #8 from llh1/master

Use message_timeout
Rename date to current_from and catch Model::NotFound exception
Rename date into current_from
Change error message
DRY
DRY
Update current_to instead of is_current
Migration for current_from and current_to
Bump version to 0.6
Merge pull request #9 from llh1/52304101_refactor_is_current_in_sample_activity_table

52304101 refactor is current in sample activity table