Add block attachment edit in admin.
Add method to resolve the file base so subclasses can customize the path.
Merge pull request #1 from isaacgrant/gauthierm-attachment-block-edit

Add method to resolve the file base so subclasses can customize the path...
Make title required.
Add default attachment icon.
Merge pull request #12 from gauthierm/attachment-block-edit

Add block attachment edit in admin.