Showcase enhancements

[heswell]

• Add datasource selector to showcase chrome. This will be used to configure a top level dataProvider, that will define source of data for all data-aware component examples.

• Support tagging examples, the tags to be available in search feature. Tags need to be parsed out from source code when nav tree/ search tree is built. Could be implemented via comments preceeding component export statements ?

• improve the visual styling of showcase

• replace existing layout components with new grid layout components