TriggerMenuMT: speedup consistency checker

• merge getL1TopoAlgToBoardMap and getL1TopoAlgToItemMap functions to avoid duplicate parsing
• move the call outside the main loop in checkL1HLTConsistency
• replace usage of regex with simple string options where possible
• document code!

This (mostly due to the second point) speeds up the menu generation of Dev_pp_run3_v1 by about 25 seconds (~15%).