Add @filter variable to the pattern template

[ftrojan]

Allow @filter variable to be used in the patterns. The usage is WHERE @filter. Each propagated table should have a list of filters eligible for that table with code names F001, F002, ... to be used in the predictor name to distinguish predictors with the same parameters and pattern but different filter.

Filter can be any logical concatenation of atomic conditions which can be of the following six types:
@dateValidColumn < @baseDate
@timeBetween(Unit, @dateColumn, @baseDate) <= value
@timeBetween(Unit, @dateColumn, @dateColumn2) <=/>= value
@nominalColumn = value
@numericalColumn <=/>= value
@anyColumn IS/IS NOT NULL

For the beginning only atomic conditions themselves can be implemented.
When building list of filter for a table, SQL statements of type SELECT COUNT(*) FROM T WHERE @filter should be evaluated and only filters meeting minimum threshold throughput should be flagged as eligible.