Fix fetching of medium-size user avatars.
Fix fetching of medium-size user avatars.

In the refactoring in 31d3b1ecc0a043e792139d39f498b27929c2d686 that
fixed live-updating of the medium-size avatar data, we started just
fetching the normal-size avatar, not the medium-size avatar.  We fix
this by changing this code path to pass in the user object and
construct the URL using that.

While we're at it, we switch to using the user ID, not the email, to
construct these avatar URLs.

rishig/zulip,shubhamdhama/zulip,jackrzhang/zulip,showell/zulip,rishig/zulip,punchagan/zulip,amanharitsh123/zulip,dhcrzf/zulip,kou/zulip,mahim97/zulip,shubhamdhama/zulip,tommyip/zulip,Galexrt/zulip,jackrzhang/zulip,andersk/zulip,brockwhittaker/zulip,eeshangarg/zulip,brainwane/zulip,timabbott/zulip,synicalsyntax/zulip,synicalsyntax/zulip,Galexrt/zulip,kou/zulip,rishig/zulip,timabbott/zulip,punchagan/zulip,punchagan/zulip,andersk/zulip,synicalsyntax/zulip,zulip/zulip,andersk/zulip,dhcrzf/zulip,andersk/zulip,punchagan/zulip,mahim97/zulip,amanharitsh123/zulip,zulip/zulip,andersk/zulip,rht/zulip,eeshangarg/zulip,tommyip/zulip,timabbott/zulip,brockwhittaker/zulip,hackerkid/zulip,eeshangarg/zulip,eeshangarg/zulip,jackrzhang/zulip,synicalsyntax/zulip,showell/zulip,rht/zulip,synicalsyntax/zulip,Galexrt/zulip,brainwane/zulip,eeshangarg/zulip,timabbott/zulip,timabbott/zulip,hackerkid/zulip,punchagan/zulip,dhcrzf/zulip,Galexrt/zulip,amanharitsh123/zulip,hackerkid/zulip,tommyip/zulip,brainwane/zulip,shubhamdhama/zulip,zulip/zulip,dhcrzf/zulip,jackrzhang/zulip,rht/zulip,dhcrzf/zulip,brockwhittaker/zulip,shubhamdhama/zulip,amanharitsh123/zulip,kou/zulip,tommyip/zulip,hackerkid/zulip,eeshangarg/zulip,dhcrzf/zulip,jackrzhang/zulip,brainwane/zulip,zulip/zulip,showell/zulip,amanharitsh123/zulip,timabbott/zulip,timabbott/zulip,showell/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,shubhamdhama/zulip,tommyip/zulip,tommyip/zulip,rishig/zulip,andersk/zulip,rishig/zulip,rht/zulip,kou/zulip,showell/zulip,jackrzhang/zulip,tommyip/zulip,rht/zulip,amanharitsh123/zulip,rishig/zulip,mahim97/zulip,brockwhittaker/zulip,Galexrt/zulip,rht/zulip,showell/zulip,kou/zulip,Galexrt/zulip,brainwane/zulip,mahim97/zulip,mahim97/zulip,punchagan/zulip,brockwhittaker/zulip,shubhamdhama/zulip,punchagan/zulip,brainwane/zulip,hackerkid/zulip,hackerkid/zulip,dhcrzf/zulip,synicalsyntax/zulip,rht/zulip,brainwane/zulip,rishig/zulip,shubhamdhama/zulip,showell/zulip,synicalsyntax/zulip,zulip/zulip,mahim97/zulip,Galexrt/zulip,jackrzhang/zulip,hackerkid/zulip,kou/zulip,andersk/zulip,brockwhittaker/zulip,kou/zulip