Revert "getItemProperty --> getAttribute"

This reverts commit 069ab59e8a730f681e4dc5f18f62b6964f698c77.

From Sebastian:

    Your code will fail if the Gallery is initialised with a JS call as in the demo:
    https://github.com/blueimp/Gallery/blob/master/js/demo.js#L84

    If you provide the Gallery elements as HTML elements, the property must be defined with the data- prefix:

    <a data-gallery="filtered" type="text/html" data-youtube="abc123abc123" title="Cool Video"></a>
remove software section
switch to data-youtube method
Revert "remove software section"

This reverts commit a2767b581d440161d8b0bf4e3d741f67f9ad6aa3.
migrate code to github