Selecting raw mode w/o loosing data (bnc#882976)

The ticket https://bugzilla.novell.com/show_bug.cgi?id=882976 explains
that we loose data if we switch from the custom proposal form into raw
proposal form.

To prevent loosing data i have integrated a confirmation dialog that
have to be accepted before we can switch to another page if we have
changed something on the current proposal form.

This solution is a shortterm solution until we get a better javascript
library with dynamic data binding to switch between raw and custom view
without a page reload and without loosing data.
+1 for Dirk's rewording suggestion; also `s/,/;/` in that sentence.