rendermanager: fixups from review

- m_batchDraws to map
- delete cosmetics
- no arithmetic in new[]
- replace irrelevant comment
- move GetSceneGraph outside of draw loop
rendermanager: drop CGUIFontTTFBase define
rendermanager: use DrawQuad to paint a window background if needed
rendermanager: turn BatchDraw into a class with setters
rendermanager: add helper Reset() function
rendermanager: rename Clear to Reset so it's not mistaken for a draw operation
rendermanager: Split BatchDraw class into a new file
rendermanager: rename BatchDraw to CBatchDraw
rendermanager: guilib cleanups

- rename to CBatchDraw
- use setter functions
- use Reset() on the batch rather than just NULL'ing the texture
rendermanager: remove unused vars
rendermanager: fix bad copy/paste
rendermanager: add getters for BatchDraw
rendermanager: use BatchDraw getters

Also drop the checks for vertices, this will be done already
rendermanager: add get/set functions for testing if a texture is current on the GPU

This lets us drop the nasty friendships with the renderers
rendermanager: use get/set gpu functions for textures
rendermanager: fixup slideshow after scenegraph/batchtexture changes
rendermanager: add BatchDraw helpers for merging similar batches
rendermanager: simplify MergeSimilar with new CanMerge/Merge functions
rendermanager: rename MergeSimilar to PreProcess in preparation for adding a few other checks
rendermanager: check for valid vertices