Support for resetting a parameter value of a component on instantiating a new child

[pgleeson]

This will be needed in various scenarios:

Changing vshift in a channel prototype when instantiated as part of a channelDensity
Setting x, y, z location of cell when instantiating a list of positioned cells
Setting v0 in a cell instance

Robert currently working on underlying issues relating to this...

[robertcannon]

There is an example of this in ex-properties.xml. If you want a property to vary from instance to instance it should be a Property and not a Parameter. Then you need an Assign element in the structure block that instantiates it in order to set its value.