Clean up .gitignore and ratCheck excludes list

Clean up .gitignore and ratCheck excludes list

- Update the .gitignore file so that the .bsp directory generated by sbt
  for the Build Server Protocol is correctly ignored by ratCheck--the
  forward slash caused problems for the sbt-rat plugin. While at it,
  remove all .gitignore entries that are related to the OS environment
  and IDE. These types of entries should go in the $HOME/config/ignore
  or $GIT_DIR/info/exclude files (man gitignore for more info).
- Removes .classpath and .keep cruft
- Updates the ratExcludes file based on the above changes. Also adds
  missing binary files for tests and windows installation that ratCheck
  doesn't alert about but should be ignored since they are expected to
  be in he repo. Also sorts the ratExcludes list for easier scanning
- Also add plugins.sbt as an exclusion in .gitignore. That file should
  not be ignored.

DAFFODIL-2430, DAFFODIL-2360