Use formhandler for forms. WIP.

Needs adaptions to stylesheets to format error messages properly.
Provide proper form error fields.
Rework form rendering to use formhandler.
Use proper auth realm for login action.
Add skeleton for reseller management.
Further work in reseller forms.

Getting closer to a first concept of handling resellers.
Use bootstrap widget to render forms.
Don't fade modal and use horizontal form.
Fix styling of error messages in forms.
Add close button to modal form.
First version of using rendering helpers.