Refactor build system

This rather large commit refactors the build system to solve a number of
problems:
- Object literal types are now declared in just one place
- There are no more circular dependencies
- There is no need for concealed subclasses in build-standalone mode

When building in standalone mode, you need to include the source in
build/src/external.  This declares object literal types as externs so
that their properties are not renamed.

When building with the application, you need to include the source in
build/src/internal.  This declares object literal types as typedefs so
that their properties can be renamed and removed.

Note also that ol.MapOptions has been merged into ol.Map, with some
renaming.

src/ol/renderer/webgl/map.js

@@ -17,7 +17,6 @@ goog.require('goog.events.EventType');
 goog.require('goog.functions');
 goog.require('goog.style');
 goog.require('goog.webgl');
-goog.require('ol.Map');
 goog.require('ol.layer.Layer');
 goog.require('ol.layer.TileLayer');
 goog.require('ol.renderer.webgl.FragmentShader');