Adding a first draft for the uglifyjs filter
Making minor changes suggested by @WouterJ
Fixing npm install for uglifyjs (wrong command, wrong version)
Fixing typo
Adding UglifyCss and changing some wording
[#2406] Proofreading new UglifyJs entry by @Sgoettschkes

* Updating some language
* Adding additional clarification details
* Updating to use UglifyJS version 2, since this is merged into Symfony 2.2, which uses an AsseticBundle that supports this Uglify version