Introduces table for attachment list
Introduces asynchronous delete for attachments
Moves attachment destroy tests to specs
Fixes wiki page attachment destroy
Adds cuke for bug
Adds changelog entry

[skip ci]
Uses let! instead of before
Refactores function implementation
Merge remote-tracking branch 'origin/feature/rails3' into bug/attachment_delete_closes_work_package_edit

Conflicts:
	doc/CHANGELOG.md
Merge remote-tracking branch 'origin/feature/rails3' into bug/attachment_delete_closes_work_package_edit

Conflicts:
	doc/CHANGELOG.md
Merge remote-tracking branch 'origin/feature/rails3' into bug/attachment_delete_closes_work_package_edit

Conflicts:
	doc/CHANGELOG.md
Merge pull request #508 from opf/bug/attachment_delete_closes_work_package_edit

[BUG] Attachment delete closes work package edit