Additional Shortcuts functionality

Some nice (imo) quality of life functionality for Apple Shortcuts.

"Create Transaction" shortcut:

- Allow creating transfers via Shortcuts.

New "Show balance for period" shortcut:
Calculates entire balance in budget book for observed period and returns amount as number.
Input:
- Budget book
- Period
Result:
- Number (total balance for budget book in period)

New "Show balance for account" shortcut:
Calculates account balance for observed period and returns amount as number.
Input:
- Budget book
- Account
- Period
Result:
- Number (total balance for account in period)

New "Show balance for category" shortcut:
Calculates category transaction sum for observed period and returns amount as number.
Input
- Budget book
- Category
- Period
Result:
- Number (transaction sum for category in period)

New "Show available budget" shortcut

Displays how much money is available in a specific budget.

Alternatively, these could all be a single shortcut action, with an option to chose the granularity (for budget book, for account, for category).