Support for new decoration border sizes BorderNoSides and BorderNone

BorderNoSides is what is known from Oxygen as "No Side Borders". The name
should indicate that there is only a border at the bottom. BorderNone is
a mode with no borders at all.

The new enums are added to KDecoration and the KCM so that all decos can
make use of it.

Aurorae is adjusted to support the new sizes for QML themes (it breaks
the old svg based themes) and Plastik makes use of it, by rendering a
one-pixel border around the window, which illustrates that it's still up
to the decoration to decide how to make use of the setting.

REVIEW: 108164