Projections enumeration level option

Introduce projections enumeration level option (ProjEnumLvl) to control the model space filtering behaviour, i.e. to choose between goals of: a) finding a maximal reduction (minimal model), and b) finding as many reductions as possible.

Levels specification

• 0 a.k.a. deep first - implement: #40 (closed),
• 1 a.k.a. balanced - current implementation,
• 2 a.k.a. breadth first - append 1P (couple) reductions to the getViableProjections results (pass ProjectionSet and add to it in getViableOATProjections and getViableOATProjectionsByDim).