#4 Need to be able to add attachments

[Stephen Holder]

Users should be able to add attachments to defects.
This is necessary for screen shots of errors, log
files, etc.
Basically, just need to add an appropriate table to
the database, and add links to the defect details
pages to add / view / remove attachments.
If no one else does it, I'll try to implement this
for the 0.7 release.