Bug #1271 - OpenLab footer not styled properly for associated group sites

Fixes for this bug include:

1) Moving a copy of the Bootstrap less core to the mu-plugins folder
2) Wrapping this core in a custom class (oplb-bs), so that on group sites and admin pages, Bootstrap classes do not conflict with native styles
3) Adding this class to divs that wrap the adminbar and footer, so that
those elements utilize the Bootstrap classes
3) Some minor styling tweaks
4) One outlying issue: for some key Bootstrap properties, the stylesheet
is compiling with the custom wrapper class repeated; the root cause is
currently unknown but should be addressed at some point. The workaround
for right now is to wrap the adminbar and footer twice.