Add complex type; slight schema refactor

[Jollyfant]

Here are some proposed changes:

• Added fdsn-complex for property of the form: [real, imag].

• Added country attribute to site property.

• Added responseStages attribute to channel. This will contain an array of responseStage elements for each consecutive response stage.

• Changed decimationFactor from general number to integer.

• Made pole & zero to plural as attribute names.

• Refactored some of the conversion script to be more in line with the current schema. Added validation of result from the conversion.