Support object/dict filtering in MetaFilter

[mshriver]

Identified in #225 when MetaFilter was added, object/dict filtering is not supported.

Related to #228 for array filtering support

metadata.params and metadata.markers are more complex data structures, and it would be beneficial for MetaFilter to provide a mechanism for filtering by this data.

One element of the complexity of these data structures is that a matching 'mark' may be on two test results at different places in the list of markers. Deterministic organization of the metadata may be necessary on import to facilitate the complex meta filtering.