Add Signature props: signatureCreationModes and signatureColorOptions

[ghost1face]

Details

Provide two new props to the PSPDFKitView component. This allows for further customization of the component to select acceptable signature modes and colors:

import PSPDFKitView, { PDFConfiguration } from "react-native-pspdfkit";

<PSPDFKitView
  configuration={{
    signatureCreationModes: [
        PDFConfiguration.SignatureCreationModes.DRAW, 
        PDFConfiguration.SignatureCreationModes.IMAGE,
        PDFConfiguration.SignatureCreationModes.TYPE
    ],
    signatureColorOptions: [
        "black",
        "#876543",
        "rgb(127, 81, 202)"
    ]
  }}
/>

Implemented both iOS and Android backings

Acceptance Criteria

• [ ] When approved, right before merging, rebase with master and increment the package version in package.json, package-lock.json, samples/Catalog/package.json, samples/Catalog/yarn.lock, samples/NativeCatalog/package.json, and samples/NativeCatalog/yarn.lock (see example commit: https://github.com/PSPDFKit/react-native/pull/403/commits/b32b4edd97ee9b49c51c8b932e2bf477744c2b24).
• [ ] Create a new release (and tag) with the new package version (see https://github.com/PSPDFKit/react-native/releases).