CMake: Build an application bundle (Wireshark.app) on OS X.

Add an ENABLE_APPLICATION_BUNDLE option which is enabled by default on
OS X and disabled elsewhere. The bundle is currently bare-bones and only
contains the main executables, Info.plist, and application icon.

Capitalize the main application name when ENABLE_APPLICATION_BUNDLE is
set and on Windows.

Start updating CPackConfig.txt for OS X packaging.

To do:

  - Add supporting libraries and frameworks.

  - Make the bundle standalone. I.e. call FIXUP_BUNDLE or
    replicate the relevant parts of osx-app.sh

Change-Id: I4e25abd3b8cbe121ec8615b98706a15c58812cdb
Reviewed-on: https://code.wireshark.org/review/4577
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Gerald Combs <gerald@wireshark.org>