Add String::Contains().

Refs #5355
Livestatus: Refactor historical tables.

Refs #5351
Refs #5348
Use std::string::find() in String::Contains().

Refs #5355
Fix some more compiler warnings.

Refs #5348
Merge branch 'fix/refactor-hist-tables-5351' into next

Fixes #5348
Fixes #5351
Fixes #5355