Clear up some USB confusion

* The USB branding is not consistent. Please take a read of the spec
  rather than random websites to provide more consistent terminology.
* The point of client-side cables is the
  single-cable-development-experience. It should be consistently
  highlighted.
* There is no "BeagleBone-X15". BeagleBoard and BeagleBone are not
  interchangable terms.
* For BeagleV-Ahead, it is important to note it is a type-AB receptacle
  because it can act as both a host and client at super-speed. This is
  the reason we put on the somewhat rare micro-AB connector--we want
  people to be able to use it both ways without violating
  specifications or requiring extensive software configuration.

cc @lorforlinux