content object: collapse add attachement
in create post/forum /announcement/..
the "Add Attachement" section takes too much space which force the user to scroll down to save eventhough in most cases the user doesn't add attachements
- makes the section collapsible
- collase it by default
- add visual clue - i.e. arrow - to show the section is collapsed
- when clicking the visual clue/section title toggle section's visibility