Signing Service initial support (bugs 1070189, 1070191, 1070227)

Bug 1070189: Call the trunion API (not tested with servers yet)
Bug 1070191: Signing management command
Bug 1070227: Script to sign all existing add-ons
Same as above regarding the "comments as sentences". Also, not sure this above comment regarding "needing some feedback" is relevant in the code here ;)