LPS-31462 Message broadcasting in staging

Hey Mike,

This is the very first portion of the messaging for staging. Since when we coded this, we have decided to get rid of some of the portlet data handlers so this concept might change a little - so I'm sending this to you to get your feedback on this instead of reviewing it.

So the idea is that the user would care for 3 levels of messages info - warning - error. The ExportImportMessage is storing this information.

We also have a factory - pretty straightforward.

Once again, I'm going to check this again tomorrow, but also wanted to get your feedback.

Thanks.

cc: @KocsisDaniel