Added a method to enabled grouping columns by array

[nibsirahsieu]

Currently, if we want to do grouping by multiple columns, we have to write groupBy for each column. For example:

FooBarQuery::create()
   ->joinBaz()
   ->select(['Foo', 'Bar'])
   ->withColumn('COUNT(Baz.Id)', 'nbBazs')
   ->groupBy('Foo')
   ->groupBy('Bar')

with this PR, we just simply write:

FooBarQuery::create()
   ->joinBaz()
   ->select(['Foo', 'Bar'])
   ->withColumn('COUNT(Baz.Id)', 'nbBazs')
   ->groupByArray(['Foo', 'Bar'])

[marcj]

Well, thanks, but Propel1 is feature freeze. You can try it at Propel2

[nibsirahsieu]

Ok, no problem :), i'm going to open PR on the Propel2 repo