Fixing 1280, credit/debit invoices flipping signs

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extra : source : 232101d449fa7dde4abb6e3f3b5969040f9517a9
Simplifying slightly the employee creation workflow

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extra : source : eb6e519e8c0191d50b6090d07cca011f21dd5891
Merge pull request #544 from einhverfr/master

Fixing 1280, credit/debit invoices flipping signs