add js url filter hook

[afragen]

We hard-coded the plugin URL. If this framework is used in a theme the JS won't be loaded. This hook allows for a simple method of returning a correct URL for enqueuing the JS file.

Hopefully, this fixes https://github.com/afragen/wp-dependency-installer/issues/29

[afragen]

Adding the filter as follows to a theme's functions.php file should properly load the JS file.

add_filter(
    'pand_dismiss_notice_js_url',
    function( $js_url, $composer_path ) {
        return get_stylesheet_directory_uri() . $composer_path;
    },
    10,
    2
);

Unfortunately I see no way to do this automatically, though I could include this filter inside the code and create another filter to return a boolean if running from a theme.

@collizo4sky let me know your thoughts.

[w3guy]

LGTM