Build json interface for weather data

[sebschmied]

Create a json request/response system to replace the current system with direct database access.

Content customizable by request:

• which values to get (timestamp, windspeed and max speed, original windspeed and original max speed, pressure, temperature, humidity)
• number of datasets to get
• datasets by time range

Features not sure if needed:

• unit conversions (knots, kph, ...)
• "api key" system to retain control of usage

Benefits:

• Easier development of new features on static/js only sites
• Less dependency on database