Merge pull request #6 from llh1/master

Fix common module for model
Fix require
Add order_id column in items table
Handle items. If we cannot find any samples info for the item being considered, just skip.
Handle sample activity in sample decoder. Executed for example when we receive a transfer tube to tube message, it adds the new sample activity.
Don't break the ancestor chain, call super
Remove uneeded method. Do not raise not found exception if no sample is found for the container
Item model
Order model
Add method sample_by_uuid
Execute set_order_id! only if @order_uuid is set
Bump version to 0.5.2
Add comments
Remove requirement to core_ext
Do not break ancestor chain
Merge pull request #7 from llh1/use_items_table

Use items table