Refactor reusable code

[gmp26]

This repo is good at making standalone Apps, but pretty hopeless at packaging reusable directives. I think we need to start a new repo for reusables modelled along angular-ui/bootstrap lines. This would mean adopting conventions such as each directive in its own [angular] module, and probably dispensing with require.js.

So we keep Apps1 for apps, but start a new repo for directives and associated support - probably by forking angular-ui/bootstrap. Those guys can summon amazing demos in plunkr or jsFiddle with very little code.

Here are some candidate reusables

Directives

1. Factor out existing d3 directives.
2. A graph plotter
3. An <input type="tex" ngModel="{{mathExpr}}" > input directive based on MathQuill
4. The mgc directives currently in incoming - these have yet to find a place in Apps1, probably because they are naturally best published as directives.

   Services

5. A TeX to abstract syntax tree parser service. (Probably can inherit this from MathQuill)
6. An adaptive function sampler service. It must take a mathematical expression and sample it intelligently over a given domain.