Kibana dev and build process for the new platform

[spalger]

See #14993 for discussion that lead to this meta ticket

Plan:

• [dev/ci_setup] generalize jenkins_setup script for other CI environments #15178 @spalger ci setup script for installing node and dependencies
• @tylersmalley move to yarn
• Kibana build tool #15055 @spalger / @kjbekkelund bootstrap script that runs yarn inside all projects (takes care of link: deps)
• Skip symlink dependencies in build kibana-plugin-helpers#57 @kjbekkelund plugin helpers remove symlinks from node_modules at build time
• Require ../kibana-extra for plugins during development #15452 @kjbekkelund move over to plugins in ../kibana-extra in development:
• Build multiple Kibana packages for production #16313 @kjbekkelund rewrite link: dependencies to local requires when building Kibana (EDIT: approach changed to relying on node_modules, see PR)
• @kjbekkelund plugin installer
  • [plugin] Handle Kibana package dependencies #16509 handles link dependencies on core packages
  • Remove --plugin-dir option from plugin cli #15191 remove the --plugin-dir flag (hasn't worked since 5.4 at least) (details)
• No longer recommend manual plugin installs #15366 @kjbekkelund update docs to be more strict about using ./bin/kibana-plugin install

Longer term, move to load plugins from ../plugins in production instead of ./plugins:

• @jbudz put kibana source (excluding optimize/config/bin) in the build output
• @kjbekkelund load plugins from a sibling kibana-extra or plugins folder
• @kjbekkelund plugin installer: install into '../plugins' relative to kibana root
• Symlink 'link:' dependencies in plugin installer #16481 @kjbekkelund plugin installer: needs to symlink the link: dependencies when depending on other Kibana plugins

[kimjoar]

Closing this as all the required tasks are done for now. Will open more specific tasks as we go.