Simplify rendering backends.

nifty-core:

- Delete BatchFactory & CoreBatchFactory, and just instaniate a
  BatchInternal & CoreBatchInternal directly, respectively, in
  BatchRenderBackendInternal & BatchRenderBackendCoreProfileInternal,
  respectively.

- Remove the BatchFactory & CoreBatchFactory parameter from
  BatchRenderBackendInternal & BatchRenderBackendCoreProfileInternal
  constructors, respectively.

Lwjgl / Jogl / LibGDX:

- Delete JoglBatchRenderBackend & LwjglBatchRenderBackend, since they
  just delegate everything to BatchRenderBackendInternal anyway. Don't
  delete GdxBatchRenderBackend because it specializes a couple of methods
  rather than delegating.

- Delete JoglBatchRenderBackendCoreProfile &
  LwjglBatchRenderBackendCoreProfile, since they just delegate
  everything to BatchRenderBackendCoreProfileInternal anyway (there is
  no GdxBatchRenderBackendCoreProfile).

- Delete JoglBatch, LwjglBatch, GdxBatch, since they just delegate
  everything to BatchInternal anyway.

- Delete JoglBatchFactory, LwjglBatchFactory, GdxBatchFactory.

- Delete JoglCoreBatch, LwjglCoreBatch (there is no GdxCoreBatch).

- Delete JoglCoreBatchFactory, LwjglCoreBatchFactory (there is no
  GdxCoreBatchFactory)

- Move remaining classes in render/batch and render/batch/core packages
  into render/ package.

- Delete batch & batch/core packages.

- Modify JoglBatchRenderBackendFactory & LwjglBatchRenderBackendFactory
  to instantiate a BatchRenderBackendInternal directly, instead of
  instantiating a JoglBatchRenderBackend or LwjglBatchRenderBackend,
  respectively.

- Modify JoglBatchRenderBackendCoreProfileFactory &
  LwjglBatchRenderBackendCoreProfileFactory to instantiate a
  BatchRenderBackendCoreProfileInternal directly, instead of instantiating
  a JoglBatchRenderBackendCoreProfile or
  LwjglBatchRenderBackendCoreProfile, respectively.

- Remove instantiation of JoglBatch, LwjglBatch, GdxBatch from
  JoglBatchRenderBackendFactory, LwjglBatchRenderBackendFactory, &
  GdxBatchRenderBackendFactory, respectively.

- Remove instantiation of JoglBatchCoreProfile & LwjglBatchCoreProfile
  from JoglBatchRenderBackendCoreProfileFactory &
  LwjglBatchRenderBackendCoreProfileFactory, respectively (there is no
  GdxBatchCoreProfile or GdxBatchRenderBackendCoreProfileFactory).

- Mark JoglRenderDevice & LwjglRenderDevice as deprecated, including
  javadoc explaining what to use instead (there is no GdxRenderDevice).