* Update ringbuffer submodule to fix includes
* Remove cyclic includes
* Remove Qt include prefixes
* Include C++ versions of C headers
E.g.: assert.h -> cassert
* Move CLIP_BORDER_WIDTH into ClipView
This allows to remove includes to TrackView.h in ClipView cpp files.
* Elliminate useless includes
This improves the include structure by elliminating includes that are
not used. Most of this was done by using `include-what-you-use` with
`CMAKE_C_INCLUDE_WHAT_YOU_USE` and `CMAKE_CXX_INCLUDE_WHAT_YOU_USE`
set to (broken down here):
```
include-what-you-use;
-Xiwyu;--mapping_file=/usr/share/include-what-you-use/qt5_11.imp;
-Xiwyu;--keep=*/xmmintrin.h;
-Xiwyu;--keep=*/lmmsconfig.h;
-Xiwyu;--keep=*/weak_libjack.h;
-Xiwyu;--keep=*/sys/*;
-Xiwyu;--keep=*/debug.h;
-Xiwyu;--keep=*/SDL/*;
-Xiwyu;--keep=*/alsa/*;
-Xiwyu;--keep=*/FL/x.h;
-Xiwyu;--keep=*/MidiApple.h;
-Xiwyu;--keep=*/MidiWinMM.h;
-Xiwyu;--keep=*/AudioSoundIo.h
```
* Fixup: Remove empty #if-#ifdef pairs
* Remove LMMS_HAVE_STD(LIB|INT)_H
