Implement an alias system for shortcuts (purls)

[craigsapp]

In the spreadsheet for the list of data that can used to create PDFs (http://bit.ly/musedata-menu), the SHORTCUT is a unique identifier for a specific PDF. This shortcut (id) should not be changed. However, create a new column called ALIASES which can be used to store alternatives to the main shortcut. If a shortcut is changed, then the old one should be moved to the ALIASES column.

The list of ALIASES are comma separated with optional spaces (or optional commas). ALIASES should be unique and not conflict with any other ALIAS on the spreadsheet or with any SHOURTCUT on the spreadsheet.