Decoding URL parameters properly in bucket strategy factory.
Made bucketing strategy configurable via query definition.

The bucketing strategy can be configured by setting the "buckets"
literal field on Categories and Histogram filters. Current options
are "log", "logQuantile" and "categorical". The "log*" strategies
can be further configured via a query string, e.g:

    <literal name="buckets" value="log?base=10&n=5&scale=0.1" />