mm: add build.gradle and add .gitignore

add gradle build system and add .gitignore .gradle/ folder

Signed-off-by: KyungKoo Kang <kyungkoo.kang@yahoo.com>
Merge branch 'master' of https://github.com/GDG-Korea/gdg_codelab_1403
Merge pull request #29 from kyungkoo/master

add build.gradle and add .gitignore