updated exit messages

[jennahamlin]

Two main changes include:

• exits if user includes the same file name for read 1 and read 2 (i.e. el_gato.py -1 testRead.R1.fastq.gz -2 testRead.R1.fastq.gz)
• updated error message and exit when more than two mompS alleles are identified or when zero mompS allele is identified