Create/Improve NumberLine

Summary: Aside from UI changes, there is an optional tick controller, and the labels can be anywhere.

Test Plan:
1) Deal with ButtonGroup, RangeInput, PropCheckBox, and ValidatedNumberInput
2) Deal with this

Reviewers: jack

Reviewed By: jack

CC: alpert, eater

Differential Revision: http://phabricator.khanacademy.org/D6903