Determine limits of dataset size that can be supported by shinyapps.io + document Amazon AWS deployment

[lcolladotor]

Using on-disk memory representations like HDF5 files as well as remotely-hosted images supported by SpatialExperiment, we should explore the limits for dataset sizes that are can be hosted on shinyapps.io. As part of #62 we should also reduce as much as possible memory usage in R. Our recommendations should be clearly stated in our documentation, likely expanding #59. As part of the unit tests, we should also memory profile the functions in spatialLIBD used by the interactive web applications.

We might also need to create a guide for deploying the interactive applications on Amazon AWS for larger datasets.