feat: improve UX of main page and filter bar

[barredterra]

• "Upload a Bank Statement" button (We primarily want to sync transactions, so this is not important)
  • Change from custom button to menu button
  • Remove from empty state
• "Auto Reconcile" button (Only works on reference numbers, which seem to be missing quite often. It wasn't clear what exactly the button does.)
  • Move to page menu
  • Prompt before execution
• Extract method get_bank_transactions and remove unused add_upload_statement_button
• Fetch bank transactions when Bank Account changes
• Show the empty state when Bank Account is unset
• Fetch bank transactions when From Date / To Date changes

Todo:

• [ ] update wiki after merge

[marination]

Rest LGTM

[barredterra]

We also got feedback from a customer who thought the "Get Transactions" button would fetch transactions from the bank. This potential for confusion will be reduced with this PR.