* Consistent license message for all the go files
* Fixing the last set of unconsistencies with the license headers
* Addressing PR review comments
* Fixing busy.go and busy_test.go license header
* tie back-end plugins together
* fix comment typo
* add tests and a bit of polish
* tests and polish
* add test, don't let backend executable paths escape the plugin directory
* Implement experimental REST API endpoints for plugins
* Updates per feedback and rebase
* Update tests
* Further updates
* Update extraction of plugins
* Use OS temp dir for plugins instead of search path
* Fail extraction on paths that attempt to traverse upward
* Update pluginenv ActivePlugins()
