Fix the Julia set shader example

[joshcol9232]

A follow-up to #3466

Hello! Ever since I added the Julia set shader example (~4 years ago!) it had always bugged me that the zoom function was never correct. This PR fixes this, and is also a general tidy-up.

In summary:

• Fix zoom issue.
• Add a COLOR_CYCLES variable to the shader to allow for cycling of the color palette. This allows for finer details of the fractal to be shown when using a high max iteration number.
• Allow user to reset the camera with "R".
• Fix some pretty terrible if statement mess.
• Other minor tidying (removal of unnecessary uniform value).
• Update copyright.

Issue

Fixes: #3465

Testing

I have tested the code on my Linux machine. I have not tested on glsl100 platforms, or Windows.

[raysan5]

@joshcol9232 Thanks for the improvement, added some possible points to review.

[joshcol9232]

@raysan5 thank you for the timely review; I've updated given the comments and also tidied elsewhere in the code where the coding conventions were not being followed. Thanks!

[raysan5]

@joshcol9232 thanks for the review!