Merge pull request #154 from christianwach/master

Fix visibility of second level menus props @christianwach
Let the Joyride Tour CSS abide the rules of the theme CSS!
Add icon for 'Request Membership' group tab.
Remove is_main_site() restriction on homepage widgets and slider.

For those using CBOX Theme on multisite, there was a restriction that only
the main site could utilize the homepage widgets and slider.

This commit removes this restriction.  Thereby, allowing site admins more
freedom to use the CBOX Theme on multiple sub-sites.

Fixes #156.