Add linkify function to qiita_pet.util
Improve study display pages

Provides links to pubmed for pubmed articles, and mailto links for users
(e.g., PIs of studies and users with whom a study is shared)

Fixes #199 by adding these columns to the dataTables on the studies pages
flake8 fix
Add suggestions from @antgonza and @teravest
Merge pull request #300 from adamrp/issue-199

Issue 199