Support plain Django Forms

[Archmonger]

Is your feature request related to a problem? Please describe.
Currently FormField only supports django.forms.ModelForm, and has no variant that works with a plain django.forms.Form

Describe the solution you'd like
Either create a variant, or have the base ColorField be a Form compatible field.

from colorfield.fields import ColorField
from django import forms

class BasicForm(forms.Form):
    color = ColorField(default='#FF0000')

Describe alternatives you've considered
N/A

Additional context
N/A

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