MIS - Student registration (Few validations added)


**Functionalities implemented:**

**1) Updated: ATs.csv**
 
   - help_text column added
   
   - validators added for mobile_number, alternate_number, and pin_code
   
   - Fields signature & 12_passing_certificate made non-mandatory
   
**2) Updated: management/commands/create_schema.py**
 
   - Code added for processing 'help_text' field of AttributeType
   
   - Appending values to list field updated

**3) Updated: templates/ndf/html_field_widget.html**
 
   - New widget added specifically for mobile/landline/pin-code field (by making use of validators field of AttributeType class)
   
     - validators field's 1st element: 'tel' value for type attribute of input element
     
     - validators field's 2nd element: regular expression value for pattern attribute of input element
   
   - Mandatory check updated for upload-file widget: Missing if-required check added

**4) templates/ndf/student_create_edit.html**
 
   - Minor css changes