Use a behavior-driven naming convention for unit tests.
Functions are now named using the pattern: [unit]__[verb]__[scenario]
The __ works as a semantic separator.
Examples:
* jid_create__returns__null_from_null()
* cmd_connect__shows__usage_when_no_server_value
Benefits:
* Easy to find all tests associated with a specific function using the
mandatory prefix.
* Test output in CI now explicitly describes the unit, the expected
outcome, and the scenario being tested.
Also disabled keyhandlers tests due to missing code in src/ui.
For example cmd_account() is located in src/command/cmd_funcs.c.
The unit test was located in tests/unittests/test_cmd_account.c.
Let's move it to a subdirectory like tests/unittests/command/test_cmd_account.c
to correpsond to the same structure.
