Fix: unpublishable config & demo-theme

[se09deluca]

Currently the configs and demo theme are publishable only if schema has been already migrated. This PR aims to make the config publishable before the schema migration.

Since the name of database depends on the config, publishing the config before schema migration gives a more linear installation flow. https://github.com/HansSchouten/Laravel-Pagebuilder/blob/26898767ef6e441909fc8a4ce2de8581a78dc617/src/ServiceProvider.php#L34

Related issue: #155

[Shaz3e]

This needs to be merged as I cannot run the command to publish the config

php artisan vendor:publish --provider="HansSchouten\LaravelPageBuilder\ServiceProvider" --tag=config