schema: refactor import_sheets, patch categories;

patch regions;
add import models, unit test passed
modify import models' fixtures
fixed import_* schema error for inheritance type
import_sheets_controller: test passed
fixed imported not saved while importing, refine models
import_sheet: refactor view
fixed import region of exists bug
import_sheet: update fixture, test passed
fixed rebase error while rake db:migrate
Merge branch 'feature/refactor_import' into develop