Added cortical action for "a = b * c"
Added comments for expected convolution result
Removed test for convolution not implements

(Since the point of this PR is to implement convoluton)
Added cortical action for "a = b * c"
Added comments for expected convolution result
Removed test for convolution not implements

(Since the point of this PR is to implement convoluton)
Refactored thalamus.py and cortical to use action_build.py
Merge branch 'cortical_convolution' of https://github.com/nengo/nengo into cortical_convolution

Conflicts:
	nengo/spa/cortical.py
Fixed dumb merging error
Merge branch 'cortical_convolution' of https://github.com/nengo/nengo into cortical_convolution
Fixed single-line nitpicks