Changes to update the German accountig charts

This update is in addition to https://github.com/odoo/odoo/pull/780

I hope everything is fine. If not please let me know.

I made 2 new files for the scheme of the accounts. So that the account numbers are seperated from the balance construction.
This is also for an easier handling with future updates.

And there are some few things to do in the ```account_charts_skr03.xml``` which are noted as todo in that file.
But this todo's don't affect the use of it. I will do this in the next few days.