Add support for countBy, min/maxBy, and avgByQuery()

[jamoore]

Requested both by Ola for IShare/ITimeline & Bernhard for counting various screen features.

• Not certain to be in 4.1
• May could use a special return type:

    class Stats {
      long count;
      long min;
      long max;
      long avg;
    };
  

[jmoore]

From Bernhard:

What particular counts are you trying to perform?

E.g. getting a plate geometry. Which could be done similar to this
query I guess:

select count(distinct w.row), count(distinct w.column) from Well w
where w.plate.id=plateId

In addition since our view of plate measurements starts at plates and
not at wellsamples that define a screen acquisition, it might be
useful to have counts of how many samples have been taken in one well.

Or how many measurements have been performed in one screen for one

particular plate.

[jmoore]

Implemented in r6432 as IQuery.projection() - still needs some shaking out.