standardize outputs with other fire models

[achubaty]

In creating a module to allow use of static maps of fire perimeters to be used with other fire modules, I've identified the need to coordinate and standardize the outputs of our various wildfire models so that this static fire module can be used with any of them.

1. the new static fire layer switcher module is here: https://github.com/PredictiveEcology/historicFires

   • By default, it reads in the NFDB shapefile and rasterizes the polygons, producing a stack of historic fire maps in .inputObjects.
   • There is only one event, which switches out [annually] the necesasry fire layers in the sim using scheduleConditionalEvent() to run it only for historicFireYears (e.g., 2011:2020).
   • To run with fireSense, there is already a parameter in the fireSense modules to control when the simulated wildfires should be proudced (.runInitialTime) -- setting it to start simulating fires the year after max(historicFireYears) allows using historic fire maps for years where we have them, and simulate fires in years we don't.
   • Another use case is to pre-generate a set of rasters using the fire model of your choice and feed this as a stack to the module (very useful to have finer control over fire regimes in simulations, e.g., to reduce variability from fire stochasticity).

2. fireSense and scfm already produce similar outputs (same object names + structures):

   createsOutput("burnDT", "data.table", desc = "data.table with pixel IDs of most recent burn."),
   createsOutput("burnMap", "RasterLayer", desc = "A raster of cumulative burns"),
   createsOutput("burnSummary", "data.table", desc = "Describes details of all burned pixels."),
   createsOutput("rstAnnualBurnID", "RasterLayer", desc = "annual raster whose values distinguish individual fires"),
   createsOutput("rstCurrentBurn", "RasterLayer", desc = "A binary raster with 1 values representing burned pixels.")

3. scfm will be updated to allow use of .runInitialTime (allow simulating fires only after some time during the simulation PredictiveEcology/scfm#28)

It would be great if we can standardize the objects (name, structure, etc.) in this module to match those used in fireSense etc. and make this module compatible with the static fire layer switcher.

[CeresBarros]

We should also add a "burnVector" -- a vector of burnt pixel IDs, i.e. a light version of burnMap,

OR a "burnDT" a data.table with burnt pixelID and year that is saved at the end of the simulation