Patch by Callum Lerwick. The opj_tcd_cblk array is one of the largest allocations...

Patch by Callum Lerwick. The opj_tcd_cblk array is one of the largest allocations, because it 		contains a bunch of static buffers. This also makes it a major source of cache thrashing. This patch allocates the buffers from the heap, and dynamically sizes them in the decoder. I have not yet managed to dynamically size  them in the encoder, getting the decoder to do it was tricky enough... I also split opj_tcd_cblk_t into separate encode and decode versions. A lot of fields were not used by both, so this cuts its size even further.