Reworked Item class and Filehandling class, and made methods.

Reworked item class and Filehandling class, and made methods. Item variables now use Property, FileHandling has method isEmpty to check if a file is empty.

changed milestone to %Code Minimal Viable Product (MVP)

added Backend label

requested review from @harrylx

assigned to @andreksv

added 60 commits

• 503b9b85...02332bc3 - 59 commits from branch frontend-testing
• eece641d - Merge branch 'frontend-testing' into 'FileHandlingAndreas'

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added 1 commit

• dadc43e7 - Removed duplicate method recurringProperty

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added 1 commit

• 4878f8a1 - Fixed readRegisterFromFile methods

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mentioned in commit dfca1846

merged