Improved Java API generation

New features

• New generated components: <paper-card>, <paper-progress>, and <paper-spinner>
• Generated component demo has been improved
• https://github.com/vaadin/flow-hello-world has been updated to better showcase that there are multiple ways of creating components
• Added generator support for cases where a property or method parameter can have multiple types
• Generated setters are fluid to allow chaining
• Event handling in generated components is now more typesafe
• All generated components are now defined to have a license header

Fixes

• HTML imports included in the initial HTML page are now placed after the polyfill
• Template parser will no longer try to load template files from the wrong location
• Missing type information is ignored instead of causing the generator to fail
• Prevent the page from being scrolled to the top already when clicking a router link
• Code blocks in generated JavaDocs are formatted properly
• Removed some cases where objects were created prematurely, most notably view instances that wouldn't be used
• Fixed some weird cases related to anchor URLs

Tutorials

• Fixed some cases where tutorial code didn't define any type parameter for the model type in PolymerTemplate implementations.
• Updated the described DOM structure to be in sync with what the Java code in Creating a Component Based on Many Elements

All changes

https://github.com/vaadin/flow/milestone/37?closed=1