Unify Admin and AsyncAdmin

Admin and AsyncAdmin differ some places:

• some methods missing from AsyncAdmin (e.g. methods with String regex),
• some methods have different names (listTables vs listTableDescriptors),
• some method parameters are different (e.g. AsyncAdmin has Optional<> parameters),
• AsyncAdmin returns Lists instead of arrays (e.g. listTableNames),
• unify Javadoc comments,
• ...