Moving C code in headers to .c files to allow includes from C++

CMakeLists.txt

inc/lektor/common.h

inc/lektor/lib/strv.h

inc/lektor/net.h

inc/lektor/queue.h

src/base/os.c

src/database/queue.c

src/lib/strv.c

src/main/server.c

src/module/module_qt_window.c

src/module/module_qt_window.h

src/module/qt_window/mpvwidget.hh

src/module/qt_window/mpvwidget_interface.cpp

src/module/qt_window/mpvwidget_interface.h

src/module/thread.c

src/module/thread.h