refactoring dirs make sure dir exists
refactoring utility backup
generate 4 dpi image when format
decouple format and preview
fix local test
remove function screenBgPage
fix util backup call error
remove layout & refactoring preview
remove useless code
fix jshint
archive dirs buggy, fix it tomorrow T~T
fix folder create bug
Merge branch 'feature/decouple_format_and_preview' into develop