Location landing page needs board-specific detail

[jace]

Related to #304, a location landing page may need board-specific text. For example this page for Bangalore in the internships sub-board:

1. Should have the title "Internships in Bangalore", not "Bangalore | Internships"
2. Should have a description that serves as a landing page for that specific board
3. Should not have a <link rel="canonical" …> pointing back to the root domain

The current Location model uses geonameid as sole primary key. This precludes more than one instance from existing. We could make it a compound primary key of geonameid and board_id, thereby requiring a board to exist for a location to be added, but perhaps this isn't a problem anymore.