[kernel] don't use boost::spirit::qi::parse() for parsing len in bulk request

Use custom _fast_ CommandHandler::toInt() implementation.
That don't do any extra stuff, just trying to convert string to int.

This didn't gave performance boost, with small number of arguments, but
this will avoid boost::spirit dependecy

And this patch reduce size of binary, in debug mode 0.7 MiB, in release
it must be something close to some KiB
[kernel] CommandHandler: add "(bulk)" into messages for bulk parsing
[kernel] CommandHandler: drop useless including boost/../trim