Closes #55

Fixes #393

* style: enforce sorting of imports

* style: alphabetize imports

* style: merge duplicated imports

* style: enforce ordering of imports

* style: sort imports in loot-core

* style: sort imports in desktop-client

* style: sort imports in loot-design

* style: manual fixes

* build: add linter to loot-design package

* style: automated fixes

* style: manual linter fixes

* Fix handling of -0 in budget summary

* Update based on review

Co-Authored-By: Tom French <15848336+TomAFrench@users.noreply.github.com>

It’s still also available as a modal when editing payees

Tests impossible dates eg
- months outside 1-12 range
- days outside valid range for a given month