simplify N64 joypad setup process for my fellow keyboard gamers

The N64 core interface for the RetroArch input settings were missing labels for the control stick and the four C buttons.  It took a long time of guesswork to sift through the various "N/A" options to eventually find which is the control stick left/right, which is C buttons up/down, etc., so I wanted to create the labels for them.  I simply must credit aliaspider for helping me through the RetroArch API in being able to make these changes.

I also renamed most of the button names (e.g. "L Button" to "L-Trigger" and re-arranged the order of the name structures to conform to the order of the N64 controller button mask signals (in order of big bit endianness, from the A button down to C-right) and renamed the "R2" button name to "C Buttons Mode" to illustrate that it is for activating the four alternatives to the C buttons (generally another analog stick for non-keyboard users unlike myself), as the "R2" name was specific to the RetroArch API and wasn't self-explanatory.