Adds the "molecular viewer" demo made during the ESRF code-camp (2014)
WIP: Add file downloading
WIP: Better path and prefs handling
FIX: use absolute path for makedirs
FIX: Add tests
ENH: Size check
FIX: Handle equiv case
FIX: Syntax
FIX: Rebase fixes
FIX: Smaller criterion
FIX: Minor refactor
FIX: Fix for new gloo
Merge pull request #170 from Eric89GXL/mol-view

ENH: Add demo-data downloading