Add validation on comments model

[ShehrozIrfan]

We need to add the validations on the comments model.

• Text is required
• Add minimum of 10 characters limit
• Add maximum of 500 characters limit

[ShehrozIrfan]

#19

[ShehrozIrfan]

Validation added on the comment model, as described above. And also the error messages are shown on Add Comment, Edit Comment and Reply Modal.
But there is only one UI Bug that needs to be fixed, is that the , is displayed while showing the error messages on the Reply Form Modal.
Below is the screenshot:

[FaheemAhmedNoor]

Hey! @ShehrozIrfan!
I want to fix this issue.