Allow viewing a photo within a tag-space

Tested-by: Mark Somerville <mark@crocodile.is> [Arch, MRI 2.1.1, Chromium 33, FF28]
Signed-off-by: Mark Somerville <mark@crocodile.is>
The navigator now sources thumbnail image paths

Tested-by: Mark Somerville <mark@crocodile.is> [Arch, MRI 2.1.1]
Signed-off-by: Mark Somerville <mark@crocodile.is>