common/quaternion: Move Quaternion into the Common namespace

Quaternion is within the common library, so it should be using the
Common namespace.

src/common/quaternion.h

@@ -6,7 +6,7 @@
 
 #include "common/vector_math.h"
 
-namespace Math {
+namespace Common {
 
 template <typename T>
 class Quaternion {
@@ -46,4 +46,4 @@ inline Quaternion<float> MakeQuaternion(const Math::Vec3<float>& axis, float ang
     return {axis * std::sin(angle / 2), std::cos(angle / 2)};
 }
 
-} // namespace Math
+} // namespace Common

src/input_common/motion_emu.cpp

@@ -85,8 +85,8 @@ private:
 
     void MotionEmuThread() {
         auto update_time = std::chrono::steady_clock::now();
-        Math::Quaternion<float> q = MakeQuaternion(Math::Vec3<float>(), 0);
-        Math::Quaternion<float> old_q;
+        Common::Quaternion<float> q = Common::MakeQuaternion(Math::Vec3<float>(), 0);
+        Common::Quaternion<float> old_q;
 
         while (!shutdown_event.WaitUntil(update_time)) {
             update_time += update_duration;
@@ -96,7 +96,7 @@ private:
                 std::lock_guard<std::mutex> guard(tilt_mutex);
 
                 // Find the quaternion describing current 3DS tilting
-                q = MakeQuaternion(Math::MakeVec(-tilt_direction.y, 0.0f, tilt_direction.x),
+                q = Common::MakeQuaternion(Math::MakeVec(-tilt_direction.y, 0.0f, tilt_direction.x),
                                            tilt_angle);
             }