Improve dependencies checks in the build process

- Rename all Find*.cmake files to uppercase, to make things more consistent,
  and fix some issues with them (notably the REQUIRED flag)

- Rename SYSTEMDDAEMON to SYSTEMD and only use the libsystemd instead of
  libsystemd-daemon because it's deprecated for a long time now

- Provide a WITH_* and WITHOUT_* switch for all optional dependencies

- Document things in the INSTALL file

Implement the PING on a server or the gateway itself

fix #2575

send_iq_result can have a "from" with just the domain name

Implement PING to in-room participant

ref #2575

Add utils::revstr

Implement PING, user to user only (XMPP and IRC side, using CTCP PING)

ref #2757

Rename iq_responder_callback_t to irc_… and add the equivalent to wait for iqs

Merge branch 'v1'

[spec] Update the URL, and do not hardcode the version in it

Escape a # in biboumi.1.md

Wrap a paragraph from INSTALL file to 79 chars

Merge branch 'v1'

Conflicts:
	CMakeLists.txt

Update spec file to 1.1

Send a proper error on IRC message 438 (nickname change too fast)

fix #2576

Use generic send_presence_error() instead of almost identical specializations

Run the service with the nobody user

Do not create a useless biboumi unix user with the RPM package

Add two missing type="error" in some presence errors

Release version 1.1

Merge branch 'v1'

Conflicts:
	src/network/socket_handler.hpp