Synthesis, characterization and investigation of antimicrobial and antioxidant activities of some new N,N´-bis-{3-alkyl(aryl)-4-[3-(2-methylbenzoxy)-4-methoxybenzylideneamino]-4,5-dihydro-1H-1,2,4-triazol-5-on-1-yl-methyl}-piperazine derivatives