Memoize prop transformation functions and specify their arguments

[naw]

Meant to be similar to reselect's createSelector, but instead of
reaching into redux state, it reaches into the component's this.

@jgautsch I tried to make reselect work inside the component, but reselect expects inputSelectors, which are functions that map state to inputs, and then pass those inputs to the transformation function.

Instead, we need to be able to map things already inside the component (such as this.props.something or this.someOtherDerivedData) into inputs that are passed to the transformation function.

There might be a way to clean up the API a little, but for now, it's pretty similar to reselect.

[naw]

@jgautsch I added a "search" feature to the basic todo app in order to demonstrate composition of derived data.

visibleTodos are todos that match the visibility filter (i.e. completed, uncompleted, or all)

matchingTodos are visibleTodos that also match the text search string.

When you change the text search, matchingTodos() is recalculated (by filtering visibleTodos), but visibleTodos does not have to be recalculated --- it just uses the memoized result.

When you add a new todo, you have to recalculate the visibleTodos(), which also triggers matchingTodos() to be recalculated, since it depends on visibleTodos().

[naw]

webpack can't seem to compile this since I moved it into its own repo. Not sure off hand why, probably something with ES6 vs ES7.