Reflect message IDs in channel MUCs

fix #3283

Add a multiline_message e2e test

Use a transaction around the DELETE + INSERT of the after_connection_commands

Otherwise we can imagine that two clients changing this value at the same
time would mix things up.

ref #3275

Add some missing include

Allow the execution of multiple commands after the IRC connection

fix #3275

Use Catch2’s single_include/ directory

Revert "C++17"

This reverts commit 3f088e7b3a1467a88e7c5ff9fb60dc4609d2bfa3.

Revert "Use std::optional<bool> instead of OptionalBool"

This reverts commit ba879a882e031d7b8503f78fe41d1210000c96ca.

Revert "Use if constexpr to make things a lot more readable"

This reverts commit d62ca9f87906be6f046fe9d07afb8bfb69c166e3.

Use if constexpr to make things a lot more readable

Use std::optional<bool> instead of OptionalBool

C++17

update docs to mention identd disable choice

follow coding style

optional identd

Add a few \n in the e2e error messages

Remove an unused function

Little doc typo

And this one (hostname -> address)

ref #3273

Rename a few “hostname” into “address”, regarding last commit

ref #3273