add Utils::QtcProcess

this is a wrapper around QProcess with these features:
- setEnvironment() takes a Utils::Environment instead of a QStringList
- instead of taking a stringlist with arguments, take a single shell
  command string which is fully compatible with the system's native
  shell (the bourne shell on unix and cmd.exe on windows) - with support
  for environment variable expansion, and subject to the shell's
  splitting and quoting rules. if the command is too complex (e.g.,
  contains redirections), it is transparently executed through a real
  shell.
- additionally, the class contains a set of helper functions for
  manipulating (constructing, splitting, etc.) shell command lines.
  in particular, it contains a shell-safe macro expander and the nested
  class ArgIterator which can be used for inspecting and manipulating a
  shell command line without going through the stringlist indirection
  (which is potentially lossy).

some of this is based on KDE code (KShell and KMacroExpander) which i
have written myself.