style: reformat C/C++ sources and headers with clang-format

Run clang-format over all project C/C++ source and header files
(.c, .cpp, .cc, .h, .hpp, .hh, .m, .mm) under app/ and tests/.
Non-source files (svg, qm, qrc, etc.) were not touched.

tests/gtest/undo_stack_test.cpp

@@ -5,7 +5,8 @@
 #include "undo/undostack.h"
 #include "undo/undocommand.h"
 
-namespace {
+namespace
+{
 class TestCommand final : public olive::UndoCommand {
 public:
 	explicit TestCommand(int *value)