Fix: avoid various error conditions with collections (Issue #91)

[zoidy]

…stent data when collection package exists

Description

• Added CC0 as the license for collections (which do not have a license)
• Delete existing folders in preservation staging storage to avoid the condition of bag metadata not updating. Essentially, this forces the metadata to be downloaded from figshare each time..
• Improved error handling for the bagging process

Fixes #91

Screenshots or additional context

Testing (if applicable)