Dashboard: create summary section

[leograba]

The summary section must be the focus of the dashboard tab. It must have the following information:

• Quantity of money available. It is the sum of all expenses, revenues, loans and investments since forever until the current date. In other words, it is how much money you have unnalocated (bank accounts + cash).
• Sum of money allocated on investments. It is the sum of initially allocated money plus profits or losses.
• Weighted average yield rate from the previous month.
• Budget x expenses. The ratio (in percentage) of money spent by expenses budget for the current month.