Add toolbarTitle Javascript API to override the iOS toolbar title

[radazzouz]

Solves #253

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Details

Adds toolbarTitle Javascript API to override the iOS toolbar title. See ConfiguredPDFViewComponent example from Catalog.ios.js.

Note: This requires to set showDocumentLabel, useParentNavigationBar, and allowToolbarTitleChange to false in your Configuration before setting the custom title.

Usage:

<PSPDFKitView
  document={"PDFs/Annual Report.pdf"}
  configuration={{
    showDocumentLabel: false,
    useParentNavigationBar: false,
    allowToolbarTitleChange: false
  }}
  toolbarTitle={"Custom Title"}
/>

Acceptance Criteria

• This API is iOS-only. It doesn't impact Android.
• This API is iOS-only. It doesn't impact UWP.
• When approved, right before merging, rebase with master and increment the package version in package.json, package-lock.json, and samples/Catalog/package.json (see example commit: 1bf805f).
• Create a new release (and tag) with the new package version (see https://github.com/PSPDFKit/react-native/releases).

[irgendeinich]

Doesn't affect Android

[nickwinder]

No changes touch windows. 👍