Add `libs`, `libs2min`, `void` and `remove` flows

`libs`:
Concatinates only. Useful for vendor files if you want them
separately and are using minified versions in developement(why?).

`libs2min`:
Concatenates only BUT transforms the source filename before like so:
path/filename.js -> path/filename.min.js
Useful if you use long versions in dev environment but want to use
minified versions of vendor files in production, have those files
around(bower!) and don't want to mess around minifying them yourself.

`void`:
Does nothing but replaces the block with new reference. Useful if you
have the same block on multiple html files but don't want to concat or
uglify it several times.

`remove`:
Does nothing but removes the block all together. Nothing is left even
not the reference.

Try them out.