Create the PDFViewPage when asked to by react native.

[nickwinder]

Fixes : https://github.com/PSPDFKit/react-native/issues/212

Details

There was a lifetime issue when navigating back and forth between views. Now we create a view when react native wants to. The unloading is still handled in UWP.

Acceptance Criteria

• 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).