Bring axis stylings more in-line with Design's stylings.
Merge branch 'master' into axis-stylings
[STYLING] Add in new colors, change axis spacings.

Specifically:
  - Add in Colors class to store (as static values) canonical Plottable colors.
  - Add in new 10-color scale. Creating a new color scale with
    new Plottable.Scale.Color() will use the new scale instead of
    creating an empty array.
  - Default plot color has been changed to Plottable.Core.Colors.INDIGO
  - Axes tick labels are now spaced farther from the tick marks
    by default to improve readability.
  - Interaction.DragBox now draws in the background of its Component.
Make gridlines have an opacity.

They should be solid, but they currently overlap the axis baseline.
Issue has been filed as #820.
Merge pull request #817 from palantir/stylings

[STYLING] Add in new colors, change axis spacings.