Microplanning: basic lexical noun choice

Allows microplanning to replace a noun with some alternatives found in the atomspace.
The first two dog@123 from the list  (dog@123, apple@123, dog@123, dog@123, water@123), which are from the first two links:
```
EvaluationLink eat@123 dog@123 apple@123
InheritanceLink dog@123 big@123
```
The two dog@123 become one word in the final sentence (ie. The big dog eats the apple...), while the dog@123 in the last link
```
EvaluationLink drink@123 dog@123 water@123
```
is mapped to a different word (ie. ... and the dog then drinks the water)