[Plugin] Explore features in Backstage (#696)

* Explore plugin

* Fixed styles and props

* Real conent

* Add Lighthouse and fix tests

* Add menu item

* Cleanup

* Change wording

* Update package.json

* Remove dead code

* Update yarn.lock

* Revert change to CODEOWNERS

* Reset yarn.lock to master

* Fix comments

packages/app/package.json

@@ -20,6 +20,7 @@
   "dependencies": {
     "@backstage/cli": "^0.1.1-alpha.4",
     "@backstage/core": "^0.1.1-alpha.4",
+    "@backstage/plugin-explore": "^0.1.1-alpha.4",
     "@backstage/plugin-home-page": "^0.1.1-alpha.4",
     "@backstage/plugin-inventory": "^0.1.1-alpha.4",
     "@backstage/plugin-lighthouse": "^0.1.1-alpha.4",