refactored out search params
factored out undo message
shifted check for both start and end date from storage to logic api
Merge branch 'master' of github.com:cs2103aug2014-w13-4j/main into pn-refactor-api
Merge remote-tracking branch 'origin/pn-refactor-api'
Shorten message for before after search
Use XOR operator instead
Merge remote-tracking branch 'origin/pn-refactor-api'