Added gradient effect to top region of easing curves.

Related to issue #160.
Included testing and support section in README.
Corrected two links.
Small edit to README.
Initial draft of load profile slot.

Related to issue #148.
Make sure longer interval is used when setting a new active mouse refresh rate.
Extra tweak to mouse refresh rate.
Make sure current direction gets updated when moved to dead zone.
Remove duplicate if statement.
Fixed some issues found by Valgrind.
Edited README.
Changed how widgets are removed from main layouts.
Corrected a change that broke the AdvanceButtonEdit dialog window.
Initial test of a stick modifier button.

Related to issue #162.
Make sure modifier button assignments are copied.
Fixed compile issue on Windows.
Moved some files. Added a JoyGradientButton class.
Moved gradient mouse wheel methods to new JoyGradientButton class.

Use old simpler method on plain JoyButton instances.