Decrease size of composite map.

Having too large maps causes texture thrashing.
Suppress creating of blend maps in Terrain class.

Since we provide our own blend maps.
This is done by overriding both Ogre::TerrainGroup and Ogre::Terrain.
Fix reference to temporary.

This could cause a crash.
Use references when possible.
Make sure to remove bridges at terrain shutdown.

This is done by using a std::function as callback.
Remove materials when surface is deleted.
Use nullptr for clarity.
Clean up page specific textures.

Some textures are created specifically for each page; these must be
removed when the page is removed.
Fix issue with null camera references.

Since the initialization order changed there was an issue with the
camera being accessed before it was initialized.
Added some extra asserts.

For things that shouldn't be null.
Measure time taken to load page.
Load nearby pages directly.
Use a strategy to load pages close to camera.

This is a better solution than trying to preload certain pages.
Remove obsolete method.

No need to do this now when we have do it in a superior way through the
page load strategy.
Only use composite map when needed.

Since the composite map uses a lot of texture memory we should only use
it when needed.
Removed PLSM2 scene manager.

As the Terrain Component now handles terrain.
Don't reference deleted value.

Some compilers can alter the value after it's deleted.
Delete pages when removing bridge.
Extend time logging.
Make the compile methods const.

Since these are called in the main thread once all data has been set up
we'll make it clearer that they are supposted to not alter anything.