exp-addFilterRule-rn: Add a filter rule
In explorase: GUI for exploratory data analysis of systems biology data

Adds a filter rule to the exploRase filter model for the given entity type

1	exp_addFilterRule(id, column, op, expr, active = T, ent_type = exp_entityType())

`id`	A unique identifier for the filter rule
`column`	The metadata column checked by the rule
`op`	The operator (<, >, ==, etc) used for checking the values
`expr`	The right hand expression against which the values are checked
`active`	Whether the rule should be immediately active
`ent_type`	The entity type of the metadata being filtered