Propagate v22r0 release notes to master

Also merges 2018-patches branch to master, fixing conflicts:

• Add release_notes_template.md
• Fix conflicts in Calo/CaloAssociators/src/CaloDigit2MCLinks2Table.cpp

• [2018-03-07 00:08] Validation started with lhcb-clang-test#882
• [2018-03-07 00:10] Validation started with lhcb-gaudi-head-py3#85
• [2018-03-07 00:13] Validation started with lhcb-head#1778
• [2018-03-07 00:13] Validation started with lhcb-tdr-test#80
• [2018-03-07 00:18] Validation started with lhcb-gaudi-head#1791

merged

mentioned in commit 8f3b3705