navigate: Use msg_list.prev/next for up/down methods.
navigate: Use msg_list.prev/next for up/down methods.

We've had rare and hard-to-track-down glitches with our
old implementation for going up and down in the message
list, which was using jQuery selectors.

We now just use MessageListData under the hood to find
our next id.

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