cjcampbell/isocat: isocat 0.2.5

Rewrote function isotopeAssignmentModel

• Function now checks for identical projections and resamples secondary models automatically.
• Multiple secondary models can be incorporated as a rasterStack.
• Replaced parallelization package with parallel::mcmapply.
• Removes bug where secondary models not created when running in parallel.

• Remove now-unnecessary import of package dplyr.
• Resolved bug in vignette example by adding 'stringsAsFactors = FALSE' to example dataframe.
• Removed defunct class test for individual IDs from meanAggregateClusterProbability function.