Updated Thalamus and Thalamus rule templates, and fixed NetworkArray addNode code

- Added "mutual inhibition" option to thalamus template (currently unable to modify mutual inhibition weight, but this is easy to add)
- Modified thalamus rule template to create combined rules if number of actions in the thalamus < 8.
  - Previously, user had to add one rule per action (i.e. one rule per internal thalamus ensemble)
  - Now, user adds one ruleset for all actions (i.e. one rule per thalamus)
- Added ArraySummedOrigin origin to NetworkArray class (used in thalamus rule code)
  - ArraySummedOrigin sums the output of the given origins (output dimension is same as each given origin dimension)
  - (Compared to ArrayOrigin) which concatenates given origins (i.e. one origin output per output dimension)
- Added warning to NetworkArray which informs users they cannot add things to NetworkArrays