Add tests and remove code to increase coverage

[thomastanck]

Some tests over the place to increase coverage.
Also removed unused code to increase coverage.

Summary of changes:

• Removed unused code:
  • Logic#setViewMode
  • Logic#setContext
  • ReaderViewUtil#resolveRelativeLinksToAbsoluteLinks
  • ReaderViewUtil#createExcerptElement
• Add tests for:
  • DateUtil
  • Logic#executeContextSwitch, which covers some other methods as well
  • DeleteArchiveEntryCommand
  • Model#setArchivesEntryBookFilePath
  • Model#hasArchivesEntry, Model#hasFeedsEntry
  • Model#deleteArchivesEntry, Model#deleteFeedsEntry (and its interaction with selected entry)

[coveralls]

Pull Request Test Coverage Report for Build 926

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+2.8%) to 90.004%

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Totals
Change from base Build 925:	2.8%
Covered Lines:	2323
Relevant Lines:	2581

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💛 - Coveralls