Re-enable avatars (buddy photos)

[smcv]

This should not be done until Gabble 0.5.13 (or at least, my patch that fixes #1967) has landed. There seems to be a bug in that code that's causing fd.o#11920, so it's a bad idea to pull it in right now.

(We're doing upstream stabilization/review work on Gabble at the moment, so it may be better to wait for that to happen before pulling in the upstream versions in any case. If it becomes urgent, please ping smcv.)

[marco]

There was also performance issues with the buddy cache right? Please don't re-enable until those are fixed. And we need to (re) add to the intro screen a way to get the photo, otherwise the feature is pretty useless.

[morgs]

Unlikely we can do this for FRS

[daf]

Currently, the presence service stores buddy information in a dict which is pickled to disk on every change. Moving to SQLite ought to improve performance.

[daf]

Eben suggests a 256x256 resolution. The UI would most likely involve taking a picture on first boot, and allow changing it via the Sugar control panel.

[Eben]

(In #3297) The hope here is to distribute avatar info in a pull fashion only, which should make the network implications much less severe.

[Eben]

The first-boot photo is covered by #3297. We should ensure that this gets into the release at the same time that does.

[daf]

(In #6910) #2738 address re-enabling avatar support in the presence service.