* 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()
* begin backend plugin wip
* flesh out rpcplugin. everything done except for minor supervisor stubs
* done with basic plugin infrastructure
* simplify tests
* remove unused test lines
