3.0: Apostrophe crashes on start if piece exists in db but is not configured in code

## The problem to solve
Hard crashing in this scenario makes it unnecessarily difficult to switch among branches that might have new/different doc types.

## Proposed solution

This should be a warning and not result in app crash

## Full output
```

Error: The aposDocs mongodb collection contains docs with the type recipe
but there is no module that manages that type. You must implement
a module of that name that extends @apostrophecms/piece-type or
@apostrophecms/page-type, or remove these documents from the
database.
at Object.manageOrphans (/Users/sdr/src/apostrophe/modules/@apostrophecms/page/index.js:370:21)
at processTicksAndRejections (internal/process/task_queues.js:97:5)
at async Object.emit (/Users/sdr/src/apostrophe/modules/@apostrophecms/module/lib/events.js:41:13)
at async module.exports (/Users/sdr/src/apostrophe/index.js:105:5)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! a3-demo@1.0.0-prealpha build: `node app @apostrophecms/asset:build`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the a3-demo@1.0.0-prealpha build script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR! /Users/sdr/.npm/_logs/2020-09-25T13_20_14_565Z-debug.log
[nodemon] app crashed - waiting for file changes before starting...
```