Set up simpleChart demo to use piecewise table construction.

Using addComponent().
Implement Utils.sortedIndex for use by crosshairs
Initial implementation of Crosshairs.
TODO:
- Styling
- Unit Testing
- Docs
- Cleanup API
Crosshair styling now set in plottable.css
Move sortedIndex implementation to osUtils.ts, include _ license
Simplify Crosshair API to minimal prototype version
add plottable.css to bower
Basic unit tests for CrosshairsInteraction
Minor change to unit test message
Root-level component no longer anchors directly to <svg>

Instead, if a user tries to anchor a component to <svg>, the component
creates a <g> under the svg and anchors to that instead. The <svg> receives
the CSS class "plottable".

Also removed sourcemap for tests because the sourcemap was interfering with
test debugging (debugger wasn't following them properly).
Remove commented line
Fix plottable.*
Merge pull request #152 from palantir/add-crosshairs

Add crosshairs
Proxy SVG dimensions to root-level <g> instead of storing it in variables

Makes more sense to put it there.
Set blanket threshold to 95%
Merge pull request #153 from palantir/root-node-anchoring

Root-level component no longer anchors directly to <svg>
Refactor Interaction so constructors have no side effects and inheritance works better.
Achieved by removing all internal calls to registerWithComponent() in constructor.
Now external caller must call this function to activate the interaction.
Fixes #155.
Merge pull request #156 from palantir/refactor-interaction

Refactor Interaction so constructors have no side effects and inheritanc...
Fix old examples.

anchor(<svg>) will only work properly if the <svg> has its width and height set first.

See #157.
Move all Component content into a content g nested under element.
This allows us to manage background and foreground appropriately.
Also fix #154, and change drag interaction so it appropriately renders in
background container.