Multi-currency support (#425)

* Initial foundational pass at multi-currency

* Default format currency

* More work on currency and exchanging

* Re-build currencies on change

* Currency import/setup

* Background job overhaul + cheaper OXR plan support

* Lint fixes

* Test fixes

* Multi-currency setup instructions

* Allow decimals in the balance field

* Spacing fix for form

---------

Signed-off-by: Josh Pigford <josh@joshpigford.com>

config/solid_queue.yml

@@ -0,0 +1,18 @@
+# default: &default
+#   dispatchers:
+#     - polling_interval: 1
+#       batch_size: 500
+#   workers:
+#     - queues: "*"
+#       threads: 5
+#       processes: 1
+#       polling_interval: 0.1
+#
+# development:
+#  <<: *default
+#
+# test:
+#  <<: *default
+#
+# production:
+#  <<: *default