Check-in and check-out dates / Contact form on each tag

This release adds some awesome features :

• check-in and check-out dates : These dates are displayed on list and can be choosen on checkout template.
• Contact form on each tag : A contact can be attached to each tag.
• Awesome tag colors, better than default bootstrap colors.
• Db saving to CSV files + API
• Db restoring from CSV +API
• Bugfixes : On issues #10, #2, #1

Massive checkout mode

A massive checkout mode has been added in this release.
In this mode, you can now checkout serveral items without choosing the tag at every operation.