Install grunt-contrib-watch
Configure grunt-contrib watch to monitor sass and html, and run jinja2 and sass:dev when changes occurr, configured livereload
Add watch to default task
Remove grunt-sass-convert
Revert "Remove grunt-sass-convert" because the refreshing problem is not caused by it

This reverts commit b3fe88a020772a9003ad43139fe5338de1405cb6.