Properly use C++11 enums everywhere.

src/Query.h

@@ -144,7 +144,7 @@ UnsignedInt primitiveCount = q.result<UnsignedInt>();
 class PrimitiveQuery: public AbstractQuery {
     public:
         /** @brief Query target */
-        enum Target: GLenum {
+        enum class Target: GLenum {
             #ifndef MAGNUM_TARGET_GLES
             /**
              * Count of primitives generated from vertex shader or geometry
@@ -210,7 +210,7 @@ q.endConditionalRender();
 class SampleQuery: public AbstractQuery {
     public:
         /** @brief Query target */
-        enum Target: GLenum {
+        enum class Target: GLenum {
             #ifndef MAGNUM_TARGET_GLES
             /**
              * Count of samples passed from fragment shader

src/Renderer.h

@@ -278,7 +278,7 @@ class MAGNUM_EXPORT Renderer {
          *
          * @see setFrontFace()
          */
-        enum FrontFace: GLenum {
+        enum class FrontFace: GLenum {
             /** @brief Counterclockwise polygons are front facing (default). */
             CounterClockWise = GL_CCW,