Hotfix/object returning null

[marksabbath]

These updates should resolve the error reported here: https://wordpress.org/support/topic/object-returning-null-wpengine-hosting/

To test this:

• Install this plugin, enable and configure it (Under the Genesis->Simple Share menu);
• Add the following code into any page in the WordPress site:

  if( function_exists( 'genesis_share_get_icon_output' ) ) {
   global $Genesis_Simple_Share;
   echo '<div class="share-icons">';
        echo '<div class="share-icons__icon"></div>';
        genesis_share_icon_output( 'icons__con', $Genesis_Simple_Share->icons );
   echo '</div>';

  It should show the icons where you added the code.

[nickcernis]

@dreamwhisper @marksabbath I think we should keep on using $genesis_simple_share now that we've changed it from $Genesis_Simple_Share, unless we see a large number of reports for it breaking functionality.

As @dreamwhisper suggested, we already know that at least one user has changed their code to use $genesis_simple_share: https://wordpress.org/support/topic/object-returning-null-wpengine-hosting/

The same user also helpfully updated the Wiki to reflect the new lowercase name, so it's now correct there too: https://github.com/studiopress/genesis-simple-share/wiki/Usage-Tips/_history

It seems fine to update the Gensis_Simple_Share_Preview class name to Genesis_Simple_Share_Preview if we want to, though. (That seems less likely to be referenced directly.)

[marksabbath]

It does make sense @dreamwhisper @nickcernis I'll close this PR and will work in another one to rename the class and file.