Implement formfield support in fields

[shosca]

• Added nice api for model_info with better repr and magics so now you can do something like this:

info = model_info(Person)
form_field = info.first_name.formfield()

• Allow overriding form class with our custom fields by passing form_class=.. or using info["form_class"]

[coveralls]

Pull Request Test Coverage Report for Build 827

• 112 of 112 (100.0%) changed or added relevant lines in 4 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.002%) to 99.935%

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Files with Coverage Reduction	New Missed Lines	%
django_sorcery/management/base.py	2	100.0%

Totals
Change from base Build 825:	0.002%
Covered Lines:	3095
Relevant Lines:	3097

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💛 - Coveralls