over time, a specific Lumiera code writing style has emerged.
The GUI, as it stood, used somewhat different conventions,
which now have been aligned to the common standard.
Basically we use GNU style, with some adjustments for OO-programming,
we prefer CamelCase, and write TypeNames uppercase, variableNames lowercase
the problem seems to be the interplay with the installed user
theme; what looks well with one theme is messed up with another
one, quite insidious.
Attempt to settle down on a set of default definitions
for borders and element background colors, which make the
Lumiera Gui "dark" but still respect the user's theme
for geometry and widget style
