Support double type metric

[navis]

We suffered some precision problems of metrics because currently it's allowed to be one of float or long type. This patch is for supporting double type metric in druid. I'm expecting BigDecimal type could be considered for next target.

[gianm]

@navis, this looks really useful! Haven't read everything yet, but initial comments:

• why not always use a DoubleColumnSelector for the DoubleSumAggregator? It's going to need to get cast into a double and added into a double anyway.
• looks at indexing time, inputType of the generic aggregator factories determines the type of the column stored on disk. this is a bit counter-intuitive! maybe something neutral like valueType would be more intuitive.
• are you expecting we would deprecate {double,long}{min,max,sum} aggregator factories in favor of the "generic" versions?
• are you using this in production?

[navis]

@gianm

• it's generally acceptable to use just double selector as input especially when the columns is already a numeric value in input row but when it's string and should be parsed into, Long.valueOf is way lighter than Double.valueOf (10x on cpu time) and also possible to loose some precisions.
• inputType is from type of column selector at first. I'm ok whatever the name would be.
• I didn't think about that. should we keep it for compatibility?
• we are using DoubleColumnSelector modified to accept double input and store it as double. I regret that because it will be a problem someday.

[b-slim]

@navis and @fjy are you guys still working on this ?
We also have some issue with precision lose and would like to see this Done. I can help reviewing or taking from you guys have stopped.
Please let me know ASAP thanks.

[dylwylie]

Closing as I believe this was covered in #4491