remove photon filter for our feed work.

appears to have to be implemented in strip-gallery, as if it's done before the_content filters it doesn't work. ok to remove in main class. since strip-gallery is run regardless, I think this may be OK.

to address issue #12
jetpack_photon_skip_image filter moved to main class

if the filter is inside the conditional to check if photon is active, it does not seem to work universally on every single image. no idea why. leaving it outside of a conditional seems to be ok
add duplicate photon remove

Photon is pushy enough that we have to remove it everywhere. Still add it back in after we are done.
Merge branch 'feature/photon-support' into develop