Mute Button and Balance Tweaks

Ok, I know I've already posted my postmortem on this prototype, and my thoughts in that post still stand, but I can't leave well enough alone.  This will be the last tweak of the project until it is incorporated into the larger solar system exploration game (and with better UI).  

The changes that were made for v2.1.2 of the prototype include the following:

• Changed the continuous laser cooling rate upgrades to be at 1 MW increments to match the power upgrade increments.  This makes managing the thermal load on the two continuous lasers more important.
• The UI of the three menu screens (Game Opening, Victory, and Mission Failure) have been modified to place all of the ancillary buttons on the left side of the screen.  Previously, the "Quit" button was off by itself on the right side.
• A mute button has been placed on all menu scenes as well as the primary gameplay scene.  The button is green when the sound is active and red when the sound is muted.  This is especially important for the gameplay scene in which the sound effect for the primary laser can be quite disruptive in public settings.  The mute feature can also be activated using the "s" key.

As always, I welcome any and all feedback.  This is a prototype built to test feasibility and features are meaningful and which are not.