Reorganize examples in Ketcher. Use simple npm demo applications

**Background**
Right now it is not clear how to use Ketcher in an external application. Current folders "example" and "demo" do not describe any usage examples

**Solution**
* Create "examples" folder
* Move "example" folder into "examples" and rename to "react-dev-app". (application is used for development)
* Move "demo" into "examples" and rename into "react-ketcher-api-app" (application is used to test ketcher api)
* Create "examples/react-simple-sa-app" (external application to use standalone ketcher from npm) which will use only ketcher-core, ketcher-react, ketcher-standalone as dependencies. No other modules. Use **NPM** for building the app
* Create "examples/react-simple-re-app" (external application to use remote ketcher from npm) which will use only ketcher-core, ketcher-react as dependencies. No other modules. Use **NPM** for building the app

Each example should contain README file with description how to use