Add birth date gating to moderation settings (#1435)

* Add birth date preference, modal to set, link in settings, and age gate in moderation

* Styling fixes for android

* Fix types

src/state/models/ui/create-account.ts

@@ -118,6 +118,7 @@ export class CreateAccountModel {
         password: this.password,
         inviteCode: this.inviteCode,
       })
+      /* dont await */ this.rootStore.preferences.setBirthDate(this.birthDate)
       track('Create Account')
     } catch (e: any) {
       this.rootStore.onboarding.skip() // undo starting the onboard