Initial text-wrapping algorithm for tick label text on axes

First crack at #357.

Uses the "telegraph" method:
 - It greedily adds characters up to a starting cutoff.
 - After the starting cutoff, if it finds a space character, it will start a new line there.
 - If it runs out of horizontal room before finding a space character, it will add on a hyphen and start a new line.
 - If it runs out of vertical room, it will truncate the last line with ellipses.

If a tick label gets broken into multiple lines, each line is put in a separate <tspan>
and moved to create the appearance of multiple lines of text (SVG does not currently
have automatic text wrapping).

Also improved the default formatter for axes so it only tries to scale numbers.
Remove extraneous <svg> from quicktest.
Adjust tests to be less senstitive to actual text wrap position

PhantomJS sometimes wraps text differently (probably due to differences in rendering).
Merge pull request #368 from palantir/tick-label-wrapping

Tick label wrapping