[AI] Add CriticalError fucntion to AI interface

[Cjkjvfnby]

When this method should be used by AI developers:
At the beginning of the AI initialization to ensure AI consistency with the game content.

What this command will do:

• It will show a notification to the user (popup windows) and allow them to continue the game or exit the main menu.
• It will fail to cause test build failure (where we execute AI)

Cases:

• Check that tech mentioned in AI are actually exists
  

  freeorion/default/python/AI/FreeOrionAI.py

  Line 100 in 1a23cd4

  TechsListsAI.test_tech_integrity()

• Check that value_refs actually exist (Not implemented yet)

As an alternative, we might have a function like startNewGame that will be called before startNewGame and resumeLoadedGame`.

[geoffthemedio]

we might have a function like startNewGame that will be called before startNewGame and resumeLoadedGame`.

I don't understand what that means. A function that will be called before itself?

What this command will do:
* It will show a notification to the user (popup windows) and allow them to continue the game or exit the main menu.

So similar to the existing error popup when universe generation has an error?

* It will fail to cause test build failure (where we execute AI)

Could you clarify that double negative? It will do nothing in test builds?

[Cjkjvfnby]

I don't understand what that means. A function that will be called before itself?

A new global function that is called by C++. It will be called before calling StartNewGame and LoadSave.

on Python side it will have content compatibility checks. If this function fails, the message will be shown.

So similar to the existing error popup when universe generation has an error?

Yes, similar to that, but with the option to pass the message.

Could you clarify that double negative? It will do nothing in test builds?

Done.
When CI tests are run and this function is failed, CI build should fail too.