Feature: Plugin.CopyBuild wipe instruction

When set to `true`, this added `wipe` property will completely remove the target directory contents (except hidden files) before copying the build files into it.

The instruction is only allowed if `directory` is **not** `/` as a tiny and very inadequate measure against unintentional destruction of the host system.
Update for PR #346 to fix PHPMD error
Merge pull request #424 from Block8/NamelessCoder-patch-2

Updated CopyBuild "wipe" option, fixes #346