Resolve "Document form fields"

I edited several templates where forms are existing. I decided to add the help_text arguments in the forms.py file where it was relevant according to me.

I added few templates fixes to avoid the footer to overflow the submitting button for the webapp creation form.

I didn't merge the webapp creation and update form because it will be done in another merge request. I decided to use the webapp creation form as the main one and did one modification in the update form just to keep track of it?

Closes #274 (closed)