improved encapsulation approach for LexSchedule and map creation; improved...

improved encapsulation approach for LexSchedule and map creation; improved algorithm for LexSchedule creation so that integer lex dims are not incremented unnecessarily when a block of code didn't contain any statements; fixed minor bugs in LexSchedule/item str methods; extracted only code related to LexSchedule/map creation (removed dependency stuff, for example) to shrink scope of this MR