allow ajax suggestions when we have a custom model

[andytwoods]

if we have a custom model (https://django-taggit.readthedocs.io/en/latest/custom_tagging.html#using-a-custom-tag-or-through-model), we don't get the lovely ajax suggestions. I suggest this modification to view.py and the below new settings parameter. TAGGIT_SELECTIZE_THROUGH = 'jobsboard.models.SkillTags'

[chhantyal]

Looks good to me, thank you for your contribution.

[chhantyal]

I made a new PyPI release with your commit https://pypi.org/project/taggit-selectize/2.5.0/