AI meta data

Work done to make AI supportpower usage slightly smarter. Refer to #5830 

Allows some basic usage rules to be defined in yaml for supportpowers.
You should avoid using floating point numbers in non-graphics code.  They can be a contribute towards game desyncs.  This code won't desync because it is run only on the host, but there's no real reason to use floats here so it would be better to just remove it (this parameter is never changed from its default value).