Add retracted notice to PMIDs

[jsstevenson]

• Add a lookup table for retracted PMIDs
• Write a rake task to update the retraction table
• Add a UI feature with a little "!" and a popup referencing the retraction (or something of that nature)

[acoffman]

For this feature, I know @susannasiebert has already done some work on the same issue in CIViC. You may be able to use some of that here. (Mostly the stuff under /server would be the relevant parts for you guys.)

griffithlab/civic-v2#1011

[susannasiebert]

We recently went through this same exercise in CIViC using Retraction Watch as our source for retraction information. PR can be found here: griffithlab/civic-v2#1011. The scraper in particular is here: https://github.com/griffithlab/civic-v2/pull/1011/files#diff-94983e536edb9717f8279d0a5e58b0f82619f1259cff4671d136924323545d73. A few notes that might be helpful if you go that same route:

1. There are two columns in the Retraction Watch spreadsheet with PMIDs: 'RetractionPubMedID' and 'OriginalPaperPubMedID'. Both should be checked against.
2. Retraction Watch has the concept of a Retraction Nature which can have values of 'Retraction', 'Expression of concern', 'Reinstatement', or 'Correction'. We decided to display these with varying degrees of importance with 'Retraction' being the only one being displayed in red while the others are displayed in yellow as a warning.
3. Other interesting columns from Retraction Watch that we decided to import are 'RetractionDate', and 'Reason'.