add missing pandoc declarations

Shaded environment and highlighting commands required for code in markdown cells

closes #4245
fix ansi coloring

scoping and command names were incorrect
use align environment, not aligned

aligned is only for when you are already inside a math environment (e.g. inside align)
test changes

- add markdown code block to test notebook
- update ansi filter test
Merge pull request #4466 from minrk/pandoc-preamble

various pandoc latex fixes

- add missing declarations to latex_base (required for pandoc-highlighted code in markdown)
- fix ansi color in latex, which didn't work in a variety of ways.

closes #4245