Add global var for {{site name}} - and give option

Add global var for {{site name}} - and give option to use this feild for site meta titles

Under setting add feild `brand_name` - inside this feild enter "Adidas"

Than for all SEO pages i can use this var for titles.

```
About us | {{brand_name}}

Why us | {{brand_name}}

```

Also usefull for CMS titles:

```
{{name}} | {{brand_name}}

```

DRY - duplicate project X - change the brand name and all SEO titles now update! (Also usefull if you want to change company name).

Dashboard