Population describe String template broken.

[Christian-B]

The template for population https://github.com/NeuralEnsemble/PyNN/blob/master/pyNN/descriptions/templates/string/projection_default.txt

has the line: Cell type : $celltype.name

yet is the Scelltype returns a dict with a name value as expected. The result is:

Cell type : {'name': 'IF_curr_exp'}.name

and not the expected

Cell type : 'IF_curr_exp'

[apdavison]

this should be fixed in #770