added max_level calcualtion for read coverage and method to update meta table with read coverage calculated
added max_level calcualtion for read coverage and method to update meta table with read coverage calculated

Ensembl/ensembl-variation,Ensembl/ensembl-variation,dbolser-ebi/ensembl-variation,Ensembl/ensembl-variation,dbolser/ensembl-variation,dbolser/ensembl-variation,willmclaren/ensembl-variation,Ensembl/ensembl-variation,willmclaren/ensembl-variation,Ensembl/ensembl-variation,dbolser/ensembl-variation,willmclaren/ensembl-variation,willmclaren/ensembl-variation,dbolser-ebi/ensembl-variation,dbolser-ebi/ensembl-variation,willmclaren/ensembl-variation,dbolser/ensembl-variation