* ref(popover): allow for popover content from the right

Popovers contents can display to the left of the trigger
and above the trigger. Add the ability to display to the
right of the trigger my adding mouseover padding. This
may be needed for tile view, depending on where the triggers
are located.

* squash: abstract common css proprties into placeholder class

All z-indexes found in css files have been moved into css
variables. If the z-index is used only once, the variable
name will be the same as the selector it is used in. If
the z-index is used multiple times, then the plain name
of $zindex# was used. This allowed a more confident
moving down of the toolbar so that the new modal dialog,
with z-index 500, could display on top of it.

#1436

This reverts commit 93648f361b.