feat(webapps/front-end-build): introduce auto-build task

This commit adds the auto-build task to the front-end build.

grunt auto-build -> automatically rebuilds sources on change, live
reloads app if opened

grunt build -> executes single run of dev build
grunt build:dist -> executed single run of dist build (including
minification and so forth)

More documentation on the tasks can be found in the updated README.md.

Related to CAM-1712