support to add sourcemap for debugging.
use upstream's solution to support multiple entry points.
move webpack config into standalone file.
simplify the gulpfile and extract hard coding values.
drop deprecated gulp plugins.
reformat the gulpfile
Merge branch 'feature/f2e-refactor'
clean all files in static dest.
integrate UglifyJs.
correct the static dest directory.
use the django rev-manifest collector.
Merge branch 'feature/f2e-cache-busting'