change validations, specs and refactor the model

we want to have validation on title and body to be on update,
description should be validated on update and when published is true

removed the body_safe, description_safe and default_value from model

updated specs
update specs and views

fixed a few specs description in blog_posts_controller_spec

updated a few views. added condition if tags are not present. used raw
for escaping body and descriptio for when they're nil

added data: { confirm: 'Text' } for delete link