Added codemirror and provieded new feedback view

core/forms.py

core/models.py

core/static/lib/bootstrap.min.css

core/static/lib/codemirror.css

core/static/lib/codemirror.js

core/static/lib/custom.css

core/templates/base.html

core/templates/core/feedback_form.html

core/urls.py

core/views.py