initial implementation of private collections

Former-commit-id: 4bcc8ad628fa48de5adb291197490117a3758f93
second round of private collections implementation

Former-commit-id: ed1c5c8383025a216a1b47edd9fceff7a68776c0
secured file downloads, added private url scheme for API

Former-commit-id: a27b2f8cc68f97f449168d4059a461b0e1098927
fixed unsecured data table api views

Former-commit-id: ffb17db102504b8ed0d8ae9e13185442edc80c6a
fixed api datatable access from views

Former-commit-id: 57932cd26b56e2820fdcb7d96d64f705feb45039
manually merge (repo filesystem issue: secured pycortex, more fixes to private collections

Former-commit-id: fcb001de3d6531fa950a9dac4c3de5304357a086
Merge pull request #1 from infocortex/enh/private_collections

Enh/private collections