5.1 release: support Firebase 5.5, multi-tab sync, function region selection, and Angular 7 - #1920

Checklist

• Issue number for this PR: Support for multiple tabs #1907, Support functions region #1874 (required)
• Docs included?: no, beta feature & don't have advanced config docs yet
• Test units included?: yes
• In a clean directory, yarn install, yarn test run successfully? yes

Description

• Allows for Angular 7 without peer dependency warnings
• Now requires Firebase ^5.5.
• Persistence settings can be passed in via the enablePersistence factory method or via the PersistenceSettingsToken injection token.
• Now that firebase/app is less broken, pull in many of the types from there.
• Allow configuration of Function region with the FunctionsRegionToken Injection Token

Code sample

imports: [
  AngularFirestoreModule.enablePersistence({experimentalTabSynchronization: true}),
  AngularFireFunctionsModule
],
providers: [
  { provide: FunctionsRegionToken, useValue: 'asia-northeast1' }
]