#240 Equalizer tweaks

Modified eq per bug/issue #240 to display current EQ band values (See screenshot for layout updates)
![equalizer update](https://f.cloud.github.com/assets/4549675/2123958/4dce37a4-9236-11e3-9fcc-ab12e852ee67.png)

Made minor changes to xul:sb-eq-band-slider to allow for a callback function for an update event.  Default value (null) and a check before execution should prevent this from impacting any other code. (If anything is actually using EQ band sliders besides the EQ)

The major change with the patch is the complete restructuring of the layout of the Equalizer dialog. All new labels use the existing CSS classes, so there should be no issues with any skins.  The layout is now flexible using spacers to align everything, so the eq doesn't fidget when the label text changes. (The components are so far only flexible horizontally.)

Any questions/concerns/comments feel free to ask.