Revert "Revert "Show attachments in admin""

This reverts commit 6d9dea7caf0a1c292cac07049e28cb38189c9766.

Conflicts:

	askbot/models/attachment.py
Avoid problems with import cycles
Limit import to avoid circular deps
Implement string for attachments
Check that there is a username before linking to profile
Split importer into methods
Improved bbcode2markdown; lost code and distorted quotes