corrected interpretation of x-y-axes

Thank you for the great idea of sharing epi-related R-code via github! Using a range of c(0.5,1) for Sensitivity I discovered an erroneous interpretaion of x and y axes. 

I added the following corrections:
1) L78: the for-loop must fill rows, not columns, because the contour() function always interprets the rows of z as x-values (see R help). 
2) L87: in the "red area plot" x and y were mixed up in the plot() statement
3) L80: by adding explicit x and y to the contour()-statement, the axes are correctly labeled if limits are >0 and/or <1
4) L85: in line 85 an German variable name was present