[2.0.0] Add financial reports

It would be convenient to receive automatically generated financial reports. These can work something like this:

• Possibility to select the period (every month there is a new report)

• Possibility in "Reminder settings" to be "Informed about new reports"

• Pre-Defined Reports for each Account, Category, etc.

• Basic structure of the report:

  • Trend (e.g. of income, expenses and account balances)

  • Comparison between income and expenses (Balance)

  • Savings Rate and average income / expenses per day / month

  • [Optional] Achievements (e.g. X months positive balance)