Added new rake tasks for running builds and tests.

- The rake tasks invoke the newly added xctool.sh script. xctool allows
  the running of unit tests on the iPhone Simulator through the
  command-line, whereas xcodebuild requires various tweaks of project
  files to ensure it works properly.

- xctool has been added to the "rake init" task to ensure everyone has
  the most updated version. This will ensure that xctool can properly invoke
  Kiwi unit tests; older versions do not work properly and invoke
  errors. In the future, it will make sense to add xctool as a
  submodule. However, since we are currently tracking the latest
  version, a submodule is more trouble than it is worth.

- Commands are now executed using Ruby's "system" function as opposed to
  "puts %x{}". The reasoning is that system will output both STDOUT and
  STDERR (as expected when running shell commands) whereas "puts %x{}"
  will capture STDOUT and then output to the screen upon completion of
  the command. We do not need capturing, and output is more useful as it
  lets us see what is happening as it happens.

Signed-off-by: Byron Sanchez <bfs5030@gmail.com>