Moved file and path related methods from StringHelper to FileHelper, renamed StringHelper byte methods not to be misused as string methods

- allows to have dynamic definition of attributes depended on the
  instance
- there was no real need for it to be static. Places that used it static
  have been refactored.

fixes #1318

PR #1340 changed/broke them

issue #1317

This reverts commit 0d8ae877.

far better than depending on fat guzzle