Resolve "Pin should show up at 1280px min"

Decreased window min width for pinned sidebar

Closes  #19171
Part of #19200

![Screen_Shot_2016-06-27_at_9.36.13_AM](/uploads/d0a87bca5af1bee808c5b1046c0ecf72/Screen_Shot_2016-06-27_at_9.36.13_AM.png)

See merge request !4947
(cherry picked from commit bbbd0e6c)