/autolink command to edit configuration (#71)

* MM-15965: cleaned up word boundary checks

- Using `\b` instead of a homebrewed word separator list
- Since `\b` does not consume, removed the second pass ReplaceAll
- Made tests more realistic by running MessageWillBePosted,
  to cover markdown inspection
- Added word boundary tests
- Cleanup

* added config commands

* fixed paths

* Legacy word boundaries and tests

* Added EnableAdminCommand config setting

Also
- fixed the help message
- fixed incorrect parsing of "false"
- moved command [un-]registration OnConfigurationChanged

* Added /autolink test, fixed deadlock,

* /autolink help formatting, style

* PR feedback: renamed multipass to canReplaceAll, commented

Author: levb

plugin.json

@@ -11,6 +11,14 @@
     }
   },
   "settings_schema": {
-    "header": "Configure this plugin directly in the config.json file. Learn more [in our documentation](https://github.com/mattermost/mattermost-plugin-autolink/blob/master/README.md).\n\nTo report an issue, make a suggestion or a contribution, [check the plugin repository](https://github.com/mattermost/mattermost-plugin-autolink)."
+    "header": "Configure this plugin directly in the config.json file. Learn more [in our documentation](https://github.com/mattermost/mattermost-plugin-autolink/blob/master/README.md).\n\nTo report an issue, make a suggestion or a contribution, [check the plugin repository](https://github.com/mattermost/mattermost-plugin-autolink).",
+    "settings": [
+      {
+        "key": "EnableAdminCommand",
+        "display_name": "Enable administration with /autolink command",
+        "type": "bool",
+        "default": false
+      }
+    ]
   }
 }