WiX installer for Wireshark

This is currently an experimental feature to provide Wireshark with an .msi installer.
It is intended to replace the NSIS installer, but needs to be a little more complete
before doing so.

(Developer) Differences/notes compared to NSIS installer:
1. You need the WiX toolset to build the installer.  See http://wixtoolset.org/releases/
(v3.10 is recommended)
2. SNMP, Radius, Diameter, and Qt translations files are harvested to be included in
the installer.  Any custom/additional files just need to be written to the appropriate
build output directory and the installer will pick them up.  NSIS required modifying
a file (custom_mibs.txt, etc) for inclusion
3. Plugin DLLs are not automatically harvested.  To include your DLL, modify Plugins.wxi
4. To build the WiX installer run:
> msbuild /m /p:Configuration=RelWithDebInfo wix_package_prep.vcxproj
> msbuild /m /p:Configuration=RelWithDebInfo wix_package.vcxproj


Known issues:
1. It does not include installing WinPcap or USBPcap (the NSIS installer does).  These
currently come as NSIS installers and it seems it would make more sense to "bundle" them
with WiX rather than include them as part of the Wireshark.msi.
2. Needs more flexible handling of VC CRT Merge module (need build script to provide
appropriate macros).  Something like (or modifying existing) FindMSVC_REDIST.cmake.
Currently only VS2013 CRT120 is supported.
3. Uninstalling previous versions.  NSIS installer did things more "manually" than Wix does
by default.  Need to merge as best as possible to handle backwards compatibility. The .msi
architecture uses an "UpgradeCode" help facilitate install/uninstall/upgrade and NSIS
installer doesn't have that.  The NSIS installer also removed whole directories instead of
just removing what it installed (still not sure if this is better or worse)


Patches welcome to address any of the issues above or improvements you think can be
made.
