add pdf controls for startpage, endpage, startoffset, endoffset and fix add challenge and edit challenge
fix labels
add pdf preview
add default values and onchange behavior
code convention compliance for css
code convention compliance for css, remove code related to vertical scroll (scribd) and code style compliance for jinja2 templates
set placeholder for pdf controls
add heading for pdf preview
set pdf_endpage to the last page number
remove colon
fix a bug!
remove remove! delete works fine!
remove preloader
pre-populate values for pdf controls
prepopulate pdf control fields
use remove instead of delete
add preview preloader
set placeholder for pdf_endoffset field
validations for pdf controls
fix a typo