Tiled Galleries: Don't require Photon in dev mode.

So that Tiled Galleries work reasonably well in dev mode, let's not require a connection for Tiled Galleries, and just not try to pass the images through Photon if we are in dev mode.
Merge pull request #521 from rase-/development-tiled-galleries

Tiled Galleries: Don't require Photon in developer mode.

Closes #427.