Helper function for multiple BiodbUrl instantiations

[pkrog]

Write a helper function that factorize the following:

urls <- vapply(id, function(x) BiodbUrl$new(url=url,                        
        params=list(chebiId=x))$toString(), FUN.VALUE='') 

Found in ChebiConn.R of biodbChebi extension package in functions doGetEntryPageUrl() and doGetEntryImageUrl().