Account Sync should happen at login, 1x per day, OR on-demand (#594)

* Add last_sync_date to accounts table

* Always sync Account after Valuation or Transaction creation, update, or deletion.

Skip sync if user clicks "sync" button without changing anything

* Sync user accounts daily based on last_login_at

app/models/family.rb

@@ -43,4 +43,8 @@ class Family < ApplicationRecord
   def liabilities
     Money.new(accounts.active.liabilities.map { |account| account.balance_money.exchange_to(currency) || 0 }.sum, currency)
   end
+
+  def sync_accounts
+    accounts.each { |account| account.sync_later if account.can_sync? }
+  end
 end