Lens stuff

Added a few lenses. They can be moved to the refractor if you want.

Used `purescript-index` for https://github.com/joneshf/purescript-thermite-todomvc/compare/paf31:gh-pages...gh-pages#diff-9f118d3cc59bcce279fc6619cd89d945R150 

Used `purescript-optic` for https://github.com/joneshf/purescript-thermite-todomvc/compare/paf31:gh-pages...gh-pages#diff-9f118d3cc59bcce279fc6619cd89d945R142