Don't set client-side defaults for SIA query params

[tomdonaldson]

The convenience search() functions for the sia module and the SIAService class specify default values for format,intersect and verbosity.

Although these defaults should not cause a problem with standard-compliant services, they are unnecessary and remove the client's ability to not specify those parameters to non-compliant services that may choke on specified values.

This use of defaults probably shows up for other dal modules, but this issue is focused on sia.

[tomdonaldson]

This came up regarding the attempted use of a registered SIA service that fails when the client specified a format value, so this change would enable the easy work around of not specifying a format value.