Support dynamic base URL

[shalvah]

• makes the workaround in Approach to multi-tenancy docs #721 work
• still needs tests (linking Add more integraion tests #717)

[deefour]

@shalvah I haven't had the time to trace $baseUrl back further yet, but I wanted to point out with the 'base_url' left as null for both scribe proper and 'try it out,' pulling in this change breaks 'try it out.'

We end up with undefined/our/endopint/path/here seemingly because scribe isn't setting up $baseUrl properly for the views.

[deefour]

@shalvah I think I sorted it, but wish to communicate in case it helps for later changelogs.

baseUrl in the scribe default index.blade.php was changed/replaced/... with tryItOutBaseUrl at some point. Our upgrade from 4.18 to 4.25 became broken because of this (we have a custom theme!), and it seems it wasn't documented in the Changelog (did I miss it)?

[shalvah]

Ah, yeah, that's from the localisation feature released in 4.25.0. #647

Sorry about that. Tbh, it's not so easy to maintain backwards compatibility for custom themes, but I'll keep that in mind going forward. Maybe I'll just add both old and new variables instead of renaming.