Add CountColumn, simpler adding of WithCounts, With

[lrljoe]

This change adds in:

• ArrayColumn

Plus the following "Aggregate Columns"

• AvgColumn
• CountColumn
• SumColumn

It also adds in some core methods which help the Aggregate Columns perform. These are available should there be a desire to use them elsewhere. Documentation for using these elsewhere will follow in a future release however!

• addExtraWith (for adding an extra "with" to the builder)
• addExtraWithCount (for adding an extra "withCount" to the builder)
• addExtraWithSum (for adding an extra "withSum" to the builder)
• addExtraWithAvg (for adding an extra "withAvg" to the builder)

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