WIP: get v8 compatibility for EXT:cal

This MR transfers all related MRs into master-branch and reveals compatibility to TYPO3 v8 for EXT:cal

• composer.json compatibility !4 (merged)
• SysCategoryUpgradeWizard !2 (merged) !8 (merged)
• TCADefinition of sys_category.icon !1 (merged) !7 (merged)
• get rid of Doctrine/DBAL/FetchMode !3 (merged)
• locaization-files missing !9