check which clients offer what services; potentially filter

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Many FDSN clients do not offer all three major WAVEFORM, EVENT, and STATION services (e.g. EMSC in #166).

To see what a client offers, you can use client.services which returns a dictionary. available services would be client.services.keys(). We should implement some sort of catch if someone has an incompatible client set for what they want.

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additional clarity:

We basically just need to throw a warning explaining that the user's selected client doesn't offer the service they are asking for and they should choose another.