Use Teletransporter Creation Location to Decide Starting Values

Closes #473 (closed).

This has two parts:

• Add a second phase to entity initialization that runs after a new entities.
• Making the teletransporter entity model use that, addressing issue #473 (closed).

The actual changes are really simple. Most of this work here was just research in how to do the first point. Partially to decide that a new virtual method, set_context_values a new partner to set_initial_values, but mostly to decide where the call should go. It went outside of EntityModel so I made the method public, it would be bad if someone called it when they weren't supposed to, but I don't see a way around that. And that is about as interesting as this issue gets.

added 7 commits

• 57f57dab...4377b07c - 6 commits from branch solarus-games:dev
• 2b03b403 - Merge branch 'dev' into 'tele-defaults', collecting updates.

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added 36 commits

• 2b03b403...4d08a0c4 - 35 commits from branch solarus-games:dev
• 3325a7b3 - Merge branch 'dev' into 'tele-defaults', fixing changelog conflict from yesterday.

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merged manually