use currencies from rates for select on add and edit views.

fix edit template to work with form directly
fixes #2

apps/transactions/forms.py

@@ -1,5 +1,7 @@
 from django import forms  
+import datetime
 from apps.transactions.models import Transaction
+from apps.rates.models import ExchangeRate
 #from datetimepicker.widgets import DateTimePicker
 #from django.contrib.admin.widgets import AdminDateWidget
 
@@ -12,3 +14,12 @@ class TransactionForm(forms.ModelForm):
         # https://stackoverflow.com/a/52702275/1632368
         #date_valid = forms.DateField(widget=AdminDateWidget())
 
+        exchangerates = ExchangeRate.objects.filter(datetime_valid__gt = datetime.datetime.today() - datetime.timedelta(days=7))
+        crypto_currencies = [(x, x) for x in sorted({ex.crypto_currency for ex in exchangerates})]
+        fiat_currencies = [(x, x) for x in sorted({ex.fiat_currency for ex in exchangerates})]
+
+        widgets = {
+            'fiat_currency': forms.Select(choices = fiat_currencies),
+            'crypto_currency': forms.Select(choices = crypto_currencies),
+        }
+