Improve transaction form

Default to no statement (fix #28)
Add link to statement on statement transaction creation
Fix textarea height

nummi/statement/forms.py

@@ -1,4 +1,5 @@
 from django import forms
+from django.forms.widgets import Select
 from django.utils.translation import gettext_lazy as _
 from main.forms import NummiFileInput, NummiForm
 from transaction.models import Transaction
@@ -50,3 +51,7 @@ class StatementForm(NummiForm):
 
         instance.transaction_set.add(*new_transactions, bulk=False)
         return instance
+
+
+class StatementSelect(Select):
+    template_name = "statement/forms/widgets/statement.html"