Check if document is valid before adding or removing annotations

[radazzouz]

Details

Fixes #194

This fixes the issue described in https://github.com/PSPDFKit/react-native/issues/194#issuecomment-482050508. In that sample project annotations were added before the document was loaded. So they were added to an invalid document.

This PR also updates our Xcode projects (RCTPSPDFKit.xcodeproj and Catalog.xcodeproj) to Xcode 10.2 and fixes warnings.

Acceptance Criteria

• Check if document is valid before adding or removing annotations.
• 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).

[radazzouz]

The actual fix is f6554fc