Changes

[565008][561721][562320][565196][564381] Documentation updates

 * Mention parameterless patterns in documentation
 * Removed removed AbstractMultisetAggregationOperator reference from
aggregator documentation
 * Documentation for imports was extended
 * A few small mistakes were fixed

Change-Id: Ie968a42267189a1a6229fea11cbcc2710ec1f508
Signed-off-by: Zoltan Ujhelyi <zoltan.ujhelyi@incquerylabs.com>