Add basework for opacity by category

A bug must first be fixed as the materials are not changed as they are
supposed to.
Merge branch 'transparency' into issue_19
Add first version of opacity per category working

This is working now on a per category basis, lots of things to fix:
    - Change category is not working
    - Strings are still some placeholders
    - Table borders
    - Change so that general sphere opacity affects the per category
      opacity.
Merge branch 'master' of git://github.com/qiime/emperor into issue_19
Add functionality for per-category opacity sliders

The visibility tab, now presents a slider for each category, each of
these categories controls the opacity for the spheres there defined.

The master opacity slider changes all these values at the same time.
Update emperor.js for all examples
Remove unused code from emperor.js
Add scaling by tab in the main GUI

This will contain one slider per each category in the mapping file.
Add updates to emperor.js and to the examples

This updated allows the scaling of the spheres on a per category basis,
a new callback has been added to respond to this behavior.

The callback from the slider takes a new value, it being the name of the
category.
Merge pull request #110 from ElDeveloper/issue_19

Add opacity per category in visibility tab
Merge branch 'master' of git://github.com/qiime/emperor into issue_105
Merge pull request #111 from ElDeveloper/issue_105

Add a new tab for scaling per category