Update OOjs UI to v0.1.0-pre (d4cfcce969)

New changes:
f6adfbc Give help content box a reasonable line height for legibility
af5d71c Remove CSS hack for positioning popupButtonWidget
c0768f9 PHP: Add missing OOUI\Exception class
76800b4 PHP: Wrap __toString() in try-catch to avoid unhelpful fatals
d399920 Revert "Followup ca6a16f: use parent selector both for hiding and showing windows"
234cd9f Revert "Show the modal overlay as soon as openWindow is called"

Change-Id: I317b4a747389de35411aca4ffdbbc2306b5b74cc
Merge "Update OOjs UI to v0.1.0-pre (d4cfcce969)"