This switches the Lumiera UI from GTK-2 to GTK-3
Unfortunately, this move breaks two crucial features, which have been
disabled for now: the display of video and our custom timeline widget.
Since both of these require some reworking, which in fact has already
started, we prefer to do the library and framework switch right away.
This too was a long-standing issue. While these practices
basically can be considered "common knowledge", experience
showed those topics are frequently unknown even to practised
programmers.
So now we have a single page dealing with all those issues of
code bloat, dependency poliferation, binary dependency resolution
and issues of transitive and circular library dependencies
Uniform sequence at start of source files
- copyright claim
- license
- file comment
- header guard
- lumiera includes
- library / system includes
Lumiera uses Brittish spelling. Add an according note to the styleguide.
