Speed up loading times of the iframes

[nikgraf]

One issue we have is that every iframe loads the iframe-client-bundle.js as well as the user-bundle.js.

The big chunk definitely is the user-bundle with the app inside taking up around 700milliseconds to evaluate:

Even in our dev example the file-size of the user-bundle is already quite large with 9.6 MB

There are several way we can try to tackle this:

• Find a way so evaluation can happen in parallel. Right now it seems like they run sequence.
• If possible leverage caching to make sure it doesn't evaluate the script in every iFrame.

First idea:

• The attribute async="true" could do the trick, but we would need to make sure both scripts (user-bundle & iframe-client-bundle) are loaded until execution.

@jantimon @mxstbr @RStankov ideas?

[nikgraf]

btw find here the first improvement (splitting client into client & iframe-client): #329