Income categories could be better

[PawanHegde]

Thank you for building this great open-source app! It's saved me a tonne of time.

I have a suggestion for an improvement. The categories for incomes and expenses are the same in the app (and static!). They make sense for expenses, but not for incomes. Medical, Food, etc. aren't useful categories for incomes. Something like Salary, Cashback, Investment Returns, Sale, etc. would be more appropriate.

Can the categories change as per the type of transaction? It'd be really great if we could create custom categories, but just this will be good enough for me.

Thank you!

[mendesahdivio]

making some updates to the constants and making the above code a little more neater