message-feed: Change message edit buttons to new style.
message-feed: Change message edit buttons to new style.

This changes the button styles for the message editing confirmation/cancel to the new button class ".button", rather than ".btn".

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