Add background color in the GUI

A color palette is now available at the bottom of the 'Options' tab;
default color is now black. The palette has offers black and white as
options but about every color with the manual color picker.

This fiexes #9
Change drawing ranges of the axes

Axes should now only be drawn on the ranges that they are described in
by the g_maximum and g_minimum values. This involved a change into the
buildAxisLines function.
Change the values of g_min and g_max for all axes

These values now have an extra padding that's relative to the size of
the spheres (6 times the sphere radius), this is with the intent of
making the axes in the plot look a little bit better. This change also
avoids cases when a sphere would be crossed by an axis line.

Test suite was updated accordingly.

Fixes #58
Merge branch 'master' of git://github.com/qiime/emperor into issue_58

Conflicts:
	emperor/support_files/emperor/js/emperor.js
Merge branch 'master' of git://github.com/qiime/emperor into issue_9
Change color formatting to always be HEX6

Not having this formatting in place was causing that some colors i. e.
FFFFFF would be converted into FFF which understood as an HEX6 is a blue
tone not white.
Fixes tests in test_format.py

This pull request was not accounting for the formatting in the
HTML_FOOTER constant.

Fixes #9
Merge pull request #64 from ElDeveloper/issue_9

Add background color in the GUI
Merge pull request #72 from ElDeveloper/issue_58

Change axes length calculation -- Fix issue 58