Multiple small refactors and improvements squashed together

Squashed commit of the following:

commit 40bd5683b067719441e54004c7c7f1198e5fd000
Author: affinehat <krs@umd.edu>
Date:   Tue Jun 17 12:35:58 2014 -0400

    Update dynamic force graph values

    Fine tuned formulas for generating charge, gravity, and link distance.

    Refactored base force graph values into defined constants to make
    changing them easier.

    Added two missing semicolons.

commit 782736649882b748c5c7a05099fb448be47200c2
Author: affinehat <krs@umd.edu>
Date:   Tue Jun 17 12:02:52 2014 -0400

    Replace indexOf() checks with explicit string equals

    Remove unused evt variable

    Replace indexOf() comparisons with ===

    Allow user to choose graph to display instead of hardcoding one

commit 8a7ead068b03766cd46163a04ff79621eb6c4662
Author: affinehat <krs@umd.edu>
Date:   Tue Jun 17 10:05:22 2014 -0400

    Refactor display variable logic

    Convert logic for setting display variable into self-executing
    anonymous function which is much cleaner

commit b179727ff2ad6ce1647f6f632da718ea9226eacb
Author: affinehat <krs@umd.edu>
Date:   Tue Jun 17 09:44:21 2014 -0400

    Remove all unused code and add comments

    All old commented code has been removed

    BASE_VALUE renamed BASE_SLIDER_VALUE for clarity

    Some top level comments added describing variables