micro: 0 -> nullptr
micro: spaces/empty lines
micro: add include guard comment to #endif
micro: first system headers, then lib, then local, and alphabetically sorted

reordering the X11 headers would break the build
micro: remove Q_OS_WIN case
remove useless actions/menus/shortcuts
micro: rename actionCollection to allActions
limit configuring actions to those that make sense
remove newsession vert/hor/quad

splitting can do the same
micro: join broken continuation lines
refactor firstrundialog

next up: remove ui xml stuff
micro: missing braces