Fix incorrect conditional styling of spreadsheet cells.

Summary:
Include the conditions default style when comparing equality and calculating the hash to reduce instances of false equivalency.

Then remove the QMap index cache since sorting on a hash an item may still produce unstable results in the somewhat unlikely case of a hash collision and it's going to take a lot of items before building and searching the map starts to be less expensive than a linear scan.

Reviewers: pvuorela

Reviewed By: pvuorela

Subscribers: Calligra-Devel-list

Tags: #calligra:_3.0

Differential Revision: https://phabricator.kde.org/D25035