Add support for supplying CSS and static slides files from active WP theme/child theme folder.

Selecting "From Current Theme" as the Slider theme will attempt to read a file in the theme/child theme directory named wp-parallax-content-slider.css. Setting display mode to "Static" will first check the theme folder for a static-slides.php file, if it doesn't exist it will load the static-slides-sample.php file from the plugin folder.