- version updated to 2.5.1
- added deassociation for file extension
Merge branch '2.5.1' of https://github.com/qreal/qreal
Modified changelog: added 2.5.1 description
Merge branch '2.5.1' of https://github.com/qreal/qreal
minor changelog fixes
Merge branch 'master' of https://github.com/qreal/qreal