Removing unused imports, fixing other -fwarn issues

Upping boundary on Shelly, to make IH compatible with Stackage

We now need to specify the numeric type and vector space explicitly
since these are given via type synonym family in `Diagram`

Use `mkHeight` instead.

Unlike the previous GHC releases, now we can simply reexport the
parsers

Print DynFlags when :set is used without arguments

Changing all image URLs in IHaskell.ipynb

Updating logo link