Implement database managing
Modify card list item design

The item now has icon, card name, and delta type
Merge branch 'design' into core

Has modified card list item design
CardDatabase: Return null if no delta is found
CardDatabase: Support delta from empty
Added database file manager
Modification with delta algorithm
Minor changes to DatabaseDelta & changed file managing
Add new interface to DatabaseDelta
Implement basic interface
Fix some formatter bugs
Fixed bugs