Recompute running balances when required

About 60% performance improvement on balance report

austax/models.py

@@ -15,7 +15,7 @@
 #   along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 from drcr.database import db
-from drcr.models import Amount, reporting_commodity
+from drcr.models import Amount
 from drcr.webapp import eofy_date
 
 class CGTAsset(Amount):

austax/views.py

@@ -16,7 +16,7 @@
 
 from flask import redirect, render_template, request, url_for
 
-from drcr.models import AccountConfiguration, Amount, Posting, Transaction, reporting_commodity
+from drcr.models import AccountConfiguration, Amount, Posting, Transaction
 from drcr.database import db
 from drcr.plugins import render_plugin_template
 from drcr.webapp import all_accounts, app, eofy_date