Improve error message when Defold sdk doesn't exist in the cloud

[aglitchman]

Is your feature request related to a problem? Please describe (REQUIRED):
Users get the following message if the Defold sdk doesn't exist in the cloud:
Cannot found platform sdks mappings for hash: 7a608d3ce6ed895d484956c1e76110ed8b78422a

It's hard to understand the meaning of that message and search engines don't find anything meaningful.

Describe the solution you'd like (REQUIRED):
Improve the text of the message, i.e. something like "Looks like the request version of the engine is too old, its sdk has been deleted recently. Download and use the latest version of the Defold engine: {link}".

Additional context (OPTIONAL):
Users in Defold chats ask about that message from time to time because they use outdated/alpha/bets Defold versions.