CHT Queries for eq catalogue db.

The purpose of this bug is to define the queries needed for the Earthquake Catalogue Tool.

Example Queries are the following:

1 - Find all events in the catalogue that have a "Mw" magnitude AND a "mb" magnitude
2 - Find all events that have agency [e.g. ISC] AND "Ms" magnitude AND a "mb" magnitude
3 - Find all events that have a Ms solution for both Agency 1 (ISC) AND Agency 2 (BJI)
4 - Find all events that have magnitude type Mw for Agency 1 (e.g. HVRD), AND magnitude type Ms for Agency 2 (e.g. ISC)

All of the above could be applied to a subset of the catalogue that is defined on the basis of time and or spatial dimension:
- events later than (e.g. 1970) or for events before (e.g. 1995), or for events later than (e.g. 1960) AND before (e.g. 2000).
- events inside polygon [Lon, Lat, Lon, Lat, ... Lon, Lat],
- events within a distance of (e.g. 300 km) from point (Lon, Lat),
- events inside polygon [Lon, Lat, Lon, Lat, ... Lon, Lat] AND with depth less than (e.g. 50 km)
- events inside polygon [Lon, Lat, Lon, Lat, ... Lon, Lat] AND with depth greater than (e.g. 20 km) AND less than (e.g. 50 km)
- events within a distance of (e.g. 300 km) from point (Lon, Lat) AND depth greater than (e.g. 20 km) AND less than (e.g. 50 km)