Add ability to group and track purchases across transactions

[VMelnalksnis]

Is your feature request related to a problem? Please describe. I guess the best name for this feature would be projects. There needs to be a way to track the total of some purchases over multiple transactions. The best examples of the top of my head would be when it's needed to track transactions for reimbursements (insurance, business trips, etc), or if you want to track how much you actually spent over a vacation or something.

Describe the solution you'd like

• [ ] Purchases can be linked to a single project
• [ ] It is possible to see all purchases linked to a project, as well as a total spent on the project.