v1.2: Always include stable channel (release)

After this commit http://review.cyanogenmod.org/#/c/65596/,
stable param isn't posted in request, so offer all stable releases by default.

Change-Id: I0b3aedacc67f0cfff16214324f35ba5356d08591
Offer stable channel only if source_incremental provided

Only CMUpdater provides source_incremental param, Hudson not.
Otherwise Hudson/changes/getdates.py generates all changelog for
stable/nightly channels. We need seperate change log for hudson.

Change-Id: I3efcf6b6314301ee49016364fb628199e512a117
Offer new updates only if development or release channel is selected

If 'All versions' is selected, offer all older releases

Change-Id: I829234a3f32c93ee2703a2029694bedd6a7ef632
v1.2.2: Offer new updates only if development or release channel is selected

Change-Id: I17d980ff15404f3c4274048e2b11c9574f803d1f
Reduce memcache usage

Change-Id: Ie9dd0e76283c09b193b9e381fbbff1703f53c449
v1.2.3: Final. Reduce memcache usage. Add example nginx config.

Change-Id: I3de9b4b225941175d3413c21b17fb5dafc6a0ce8