cumulative_footprint: Plot the cumulative footprint at specified levels.
In SurfClam/bio.surfclam:

Function will accumulate the footprint at specified time lags

1 2	cumulative_footprint(CatchData, SelBank, stat = "footprint", Banksize = NA, lagtime = 5, returnData = FALSE)

`CatchData`	is average catch per year. Columns are ordered as "Year" "se" "sd" and "CPUE". CPUE is the mean CPUE in a givne year. Note the required input can be generated by the CatchTable function
`SelBank`	a numeric delimiter of the assessment region (1 = Banquereau and 2 = Grand Bank).
`stat`	variable defining whether the plot will have the percent of the bank covered ('percent') or the spatial footprint ('footprint' : DEFAULT)
`Banksize`	Coverge in square km of the bank curated by the Catchdata- catch table function.
`lagtime`	is an integer or vector of integers specifying the desired lag-times in years (default = 5 years)