hydrogs

When the Income Statement is in mode `at market value`, it would be nice to have a computed account for the unrealized gains generated during the filtered time.

I dropped the asumptions of account names in the plugin [rebudget](https://github.com/scauligi/refried/blob/master/refried/plugins/rebudget.py) and the extension [avail_ext](https://github.com/scauligi/refried/tree/master/refried/extensions/avail_ext). They now accept any root name. As the `refried.is_account_account()` function needed to be modified, I...