Prepare earnings module
Cleanup
Remove useless typedef
Implement earning module
Implement display of earnings in the year overview
Merge branch 'develop' into feature/revenue

Conflicts:
	src/overview.cpp
Refactorings
Add support for earnings
Take special start months into account in budget calculation
Merge branch 'feature/revenue' into develop
Refactorings
Make sure an account is not deleted if there are still some earnings or expenses linked to it
Complete the help
Create a configuration file to store the current version of the data file system
Add an expiration date on each account
Implement the archive command
Show only the accounts of the current month
Show only current accounts on the default show command
Add command to display all the accounts
Update help
Prepare method to get all the accounts of a specific month