[UI Framework] [K7] Cherry-pick generator and doc site improvements (e…

…lastic#13479)

* Rename tasks to createComponent and documentComponent.

* Reference correct src paths in README.

* Add children and className to templates' propTypes.

* Add default folder name for page demo.

* Add suffix to sandbox routes.

* Specify testPathIgnorePatterns more clearly.

* Rename component.test.js to test.js so that Jenkins won't try to run it.

* Update npm scripts to depend on local yo dependency, not global.

* Add ui_framework/src to copy task.

* Simplify npm scripts and remove requirement for installing Yeoman from README.

* Mock out static files when running in Jest (elastic#13315)

* Add services to moduleNameMapper in jest config.