Create a /packages/:package/tarballs view

A simple view containing all tarballs of a package. Fixes: #96.
Rename tarballs to debian-monitor
Rename debian-monitor to distro-monitor
Permit building hackage-server with GHC 7.4.2
Support branches and tags for Mercurial in sourceRepositoryToHtml (fixes #104)
Add links to candidate maintenance page via template (see #72)
Implement package candidate deletion via GET/POST (see #72)
Merge pull request #110 from jwiegley/master

Permit building hackage-server with GHC 7.4.2
Merge pull request #114 from adamgundry/master

Support branches and tags for Mercurial in sourceRepositoryToHtml (fixes #104)
Merge pull request #108 from nomeata/issue96

Create a /packages/:package/distro-monitor view
Merge pull request #115 from adamgundry/issue72

Implement candidate maintenance (fixes #72)
Add travis-ci config