When DAALA_EC is enabled, calls to aom_read_tree() and aom_write_tree()
 would automatically convert the aom_tree_index and aom_prob into a CDF
 and call the aom_read_cdf() or aom_write_cdf(), which causes an
 error if DAALA_EC is enabled without EC_MULTISYMBOL.
This patch moves the conversion functions from daalaboolreader.h and
 daalaboolwriter.h into bitreader.h and bitwriter.h respectively, and
 only calls the conversion functions if EC_MULTISYMBOL is enabled.
This allows DAALA_EC to be enabled without EC_MULTISYMBOL and is a
 bitstream change when both ANS and EC_MULTISYMBOL are enabled as calls
 to read and write trees will automatically be converted into calls that
 read and write cdfs.

Change-Id: Id2f9aa9b5113292998cadfe69e4ba547324643ac