Create queries for expenses

[TobiasH05]

Make the rest of the queries in the expenses dashboard page. Also add comments describing the behavior, so usage in future is easy (see existing query). Use tempSdk for now, and write docs describing the function the sdk needs for the queries to work.

The following queries will need to be added:

• Get all accepted expenses
• Get all rejected expenses
• Add new expense
• Accept expense
• Reject expense