Correct SQL requirements for v/u_speed

[peterdesmet]

The conditions for avg_u_speed and avg_v_speed are currently:

    CASE
        WHEN avg(b.radial_velocity_std) >= 2 AND avg(b.bird_density) >= 10 THEN round(avg(b.u_speed)::numeric,5)
        ELSE 0
    END AS avg_u_speed,
    CASE
        WHEN avg(b.radial_velocity_std) >= 2 AND avg(b.bird_density) >= 10 THEN round(avg(b.v_speed)::numeric,5)
        ELSE 0
    END AS avg_v_speed,

But those WHEN requirements should actually be stated per altitude and radar, not on the average.

• [x] Have requirements per radar
• [x] Have requirements per altitude in a specific altitude band
• [x] Sum speed from the altitudes that met requirements / divided by number of altitudes that met requirements (=> those not contributed are not affecting average)
• [x] If none of the altitudes meet the requirements: set to zero

[peterdesmet]

Should these updates be included in the current visualization?

[peterdesmet]

I only want to update this in the full query, not for each CartoDB call, therefore blocked by #86.

[peterdesmet]

@hvangasteren, please review the new query. It does not yet include bird density.

[peterdesmet]

Query has been reviewed and described