search: give each Search instance an Entropy encoder (no output changes)

This essentially relocates the "active" entropy coder used during all analysis
from CTURow to ThreadLocalData. This actually reduces the number of Entropy
instances in the encoder, and solves the problem of sharing the entropy coder
between worker threads cooperating on the same CTU.
search: white-space nits
quant: pass entropy instance through init function
search: reorder nits, no effect

do allocations after simple configurations