Merge pull request #21 from guillaume-mixi/master

proguardの設定変更の問題を修正
Fix project proguard settings

proguard config file was removed in 49100af
but still referred to in project properties file.
Merge pull request #22 from hidey/hotfix_proguard

Fix project proguard settings
Fix FormFile type

FormFile is returned to the web as part of FormPictureSelectResult, hence
it itself is a Result.
Since it will be converted to JSON as such, if not implementing Result it
will be missed by Proguard settings and be obfuscated (and the JSON keys
will be the obfuscated names instead of the original variable names...).