Fetch directives scripts after client-side navigation

[SantosGuillamot]

In the same way we support css in client-side navigation, new scripts should be fetched when navigating. Right now, if we navigate to a page with a new interactive block that wasn't present on the initial page, it may not work as expected, as the behavior defined in the store of that particular block won't be available.

For example, in this movies demo, if we land on the homepage and navigate to a movie page, the media tabs (a block only present in the movies pages) won't work because the actions needed haven't been defined.