Remove unecissary core tests

All output testing is handled in compiler_test. There's not really a
good reason to double check.
Add CSSMediaQuery type

Using meta data for media-queries turned out to be a bad idea.
Entirely. It added an extra layer of complexity that could simply be
avoided by creating a new type.
Clean up util namespace
Reimplement at-media to use CSSMediaQuery, fix font-family fn
Clean up compiler

The patch removes a lot the unecessarily complex code around
expand-stylesheet by using mapcat instead of loop/recur to maintain a
level list of expressions before rendering. To do this we submit that
any type implementing the IExpandable protocol should return a level
list.

Also since CSSMediaQuery is now it's own type it is much easier to
understand what is happening instead of adding custom logic around meta
data checking.

Also, by default stylesheets are pretty-printed instead of compressed
and a CSSMediaQuery print-method was added to garden.repl.
Add garden.repl to user namespace