settings: Fix missing target=_blank on realm emoji images.
settings: Fix missing target=_blank on realm emoji images.

This resulted in problems with the desktop app, where clicking these
links would leave the user in a situation where they needed the "back"
button in order to get back to the webapp.

Fixes zulip/zulip-electron#342.

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