Port to glitch flavour

[polyamAdmin]

Ports the following changes to glitch flavour:

• 0e2a7d457cb946ae7d8c99cc5ca8e03022755ebd
• 078114c54bb8af3a3ccccfd5f8f41a8c557dcdea (reactions-bar margin)
• 39290d4e7ce63b0d1020e3b7ce5198d736baa700
• 6441457e31bd8793a0504767c540b93b14cf6623
• 7954f81d894d5925cc077780312cc3201efb8d90
• 7db119be1a056694663b3263faf333954f2e3715
• d53b129e6005b6735dec0e92548e5cd4ca65e335
• c8d3ed6b33c348f53778f24b6cf8c4db9a76cfce (Follow-up to 7954f81d894d5925cc077780312cc3201efb8d90)
• c43ae473bcf48a29af6dcf180c24cd3448a081f3

[polyamAdmin]

At some point I should align the reactions code with the one in the polyam flavour. I originally intended to just periodically re-merge the upstream PR, but some of the changes are rather puzzling.