Improve error management in the SVN Application

SVN Application seems to have limited management of the errors on commit, the commit can fail and no appropriate message would be displayed to the user.

softec had the following issue (translated by me from french):

I had to fight with the SVN App, it was not making the commits while saying that it did
The only thing was that the commit line appeared on the screen, you were seeing: $svnr.commitFiles(....
And in the log i had groovy that said that it didn't find some delta function or something
In the end, a restart of XWiki set everything back in order
it was like the svnlib was not really the good one anymore
In short, what's not cool is that it is very little visible

We need to audit the SVN Application and make sure that the error reporting is properly done, that we display proper error on the screen if a commit fails.