Add Component<P> class

This allows declaring a parameter or variable as a general "component with props P" instead of needing to declare it class based or function.

types/react/index.d.ts

@@ -26,6 +26,7 @@ declare namespace React {
     // ----------------------------------------------------------------------
 
     type ReactType = string | ComponentClass<any> | StatelessComponent<any>;
+    type Component<P> = ComponentClass<P> | StatelessComponent<P>;
 
     type Key = string | number;
     type Ref<T> = string | ((instance: T) => any);