## What changes were proposed in this pull request?

Add a check-cran.sh script that runs `R CMD check` as CRAN. Also fixes a number of issues pointed out by the check. These include
- Updating `DESCRIPTION` to be appropriate
- Adding a .Rbuildignore to ignore lintr, src-native, html that are non-standard files / dirs
- Adding aliases to all S4 methods in DataFrame, Column, GroupedData etc.  This is required as stated in https://cran.r-project.org/doc/manuals/r-release/R-exts.html#Documenting-S4-classes-and-methods
- Other minor fixes

## How was this patch tested?

SparkR unit tests, running the above mentioned script

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes #14173 from shivaram/sparkr-cran-changes.