Merge pull request #5 from dtan4/history_activity-2

[WIP] Show card history on HistoryActivity
Cut create-database branch
Create History table
Save recent history
Add created_at field to save timestamp
Merge pull request #7 from dtan4/create-database

Create database
Cut scan-activity branch
Create ScanActivity, scan card on it
Merge pull request #10 from dtan4/scan-activity

Add ScanActivity
Cut cardlist-activity branch
Show card list by felicaId
Show history by clicking list item
Merge pull request #11 from dtan4/cardlist-activity

Add CardListActivity
Do not push any history if historyList is empty
Cut show-diff branch
Show difference of balance
Colorize balance diff
Merge pull request #12 from dtan4/show-diff

Show difference of balance
Move Activity files to activities directory
Remove unused import