accessibility: Add button role and tabindex to sender names.
accessibility: Add button role and tabindex to sender names.

This facilitates interacting with them via keyboard.

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