Adding fieldsets and custom form templates

Create a custom form template file so we can custom form html as needed.
Add fieldsets to create post form, and pass name to templates.
Set form class and id through JS / config instead of template.
Refactor media-bar css so its easier to add new icons

Move the font-size and color rules to general .select-icon based
selectors,
rather than having them tied to .upload-* selectors.
Make media-bar links have larger clickable area

Move sizing from li.select-icon tags onto <a> tag, rearrange padding to
work.
This seems more sane to me, now more than just the icon is clickable.

ping @middle8media for a review on this.. I'm not sure if this is a sane
behaviour on mobile or not..
Show/hide fieldsets based on media-bar buttons

All fields sets are hidden by default, we show/hide them based on an
'active' class. We're using the href on each media-bar link to target
the fieldsets.
Also adds a 'permissions' media bar button, similar to crowdmap
Make header create button link to posts/create
Update CSS files from SCSS