added about page

Created by: jojosch

see #1993 and #2158

Questions:

• is there a function/variable to get the admin email?
• should the /help index action redirect to the about index action?
• any more output on about page?

New Features:

• Add about to dashboard navigation
• Add about to sidebar on bottom
• Add about to main navigation
• Moved help-OL to partial.
• Included help-OL-partial in about page

About & Help icon in top navigation:

About & Help in sidebar navigation on dashboard

About page with help-ol partial