[WIP] Feature/dashboard - Proof of concept

:warning: Unstable, experimental version of dashboard for saleor

Needs improvements.
If forms are independent I will wrote some think like:

```python
ctx = {}
forms = {'form': form, 'variant_formset': variant_formset, 'image_formset': image_formset}
if all([f.is_valid() for f in forms.values()]):
    do_stuff()
ctx.update(forms)
```