Update for decoding comparison with more accurate agreement estimation
Cache of decoder for 1 and n channels, orientation prefs, plot these

Added analysing/get_best_nchans.m which caches the 500ms spike
count decoding performance for individual channels incremental
numbers of channels (adding the best channel each time).

Added analysing/get_orientationprefs.m which caches the
orientation prefernces for Blanco only (at present), as indicated
by Xing.

Also a couple of new functions which plot these.

Have two versions of plotting/best_decode_ch_sess[2].m which is not
named consistent with previous plotting functions. Could do with
tidy up. Also poorly commented.
Pearson R correlation coefficient

New functions for processing and plotting the Pearson R correlation
coefficient (a measure of the noise correlation between pairs of
channels).

_sess does this on a per session basis
_tw does this for groups of 1400 trials using twc_remixer.m

twc_remixer.m creates groups of N trials with the same number of
trials for each condition throughout. The next group has completely
different trials with no overlap (some trials will be ommitted at
random). This means there is more consistency when comparing data
from different stages of learning.