Update to SPFx 1.9.1

• Upgrade to SPFx 1.9.1
• Angular v6, v7 support added
• SPFx-uifabric-themes add-on added
• TypeScript support for 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5
• Support for library component

Includes

• Office UI Fabric - 5.x, 6.x, 6.x Fluent
• pnp/pnpjs - 1.3.5
• pnp/spfx-property-controls - 1.16.0
• pnp/spfx-controls-react - 1.14.0
• jQuery - 3.4.1
• webpack-bundle-analyzer - 3.4.1
• Handlebars - 4.1.2
• Vue - 2.6.10
• Office 365 CLI - 1.23.0
• StyleLint - 10.1.0