Improved system status

This time it can't have conflicts yeee :dancer: 

1) Added few settings in the section **Settings**
2) **Environment** section is now divided in **WordPress** and **Server**
3) Added **Has custom.css** in the **Theme** sections. I think it's really useful for the support team
4) Added a link in **Templates Override** section which links to the article by @BFTrick about how to update outdated templates (appears only if there are outdated templates)
5) Removed icons in favor of *[?]* in a proper td. Links are not clickable.
6) Added a link to the codex about how to create a child theme (appears only if you are not using one already)
7) Displays wether or not a plugin is network enabled