Add Photon Medium ID selector to LLP1 derivation

This MR adds an algorithm which adds a boolean for photons passing Medium ID into the derivation. Potentially useful for LLP analyses, as the Tight photon ID WP has been shown to bias significantly against non-pointing photons. In particular this is helpful for those analyses relying on the g35_g25_medium trigger.

I tested the effect on file size with a ttbar sample:

mc21_13p6TeV.601230.PhPy8EG_A14_ttbar_hdamp258p75_dil.merge.AOD.e8453_e8455_s3873_s3874_r13829_r13831

	Before Change	After Change	% Change
FILE SIZE (Kb) / event	73.339	73.383	.059%

Please have a look @longjon @jburzyns