Background gradients will be ignored on jQM 1.4 and over. Fixes #148.

Hi~!
I'll a PR to fix #148.

As discussion for #148, on jQM 1.4 and over, background gradients will be ignored and gradient controls(gradient slider bar, "+" button, and input box for START color and END color) is removed on left Swatch panel/menu.

If there are any problems or mistakes on that PR, please let me know.
Thanks in advance.