doc: fix 404 link of BUILDING.md
https://boxstarter.org/WebLauncher is 404, change to https://boxstarter.org/weblauncher which is accessible now.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
https://boxstarter.org/WebLauncher is 404, change to https://boxstarter.org/weblauncher which is accessible now.