NSIS installer generated by MSBuild

The new installer.csproj will generate a setup for GAC/DDEX installation (using NSIS).
The output file name is like *Setup_Npgsql-2.2.0-rc2.exe*

Use **Release-net45** (Npgsql2013.sln) configuration.
It will generate setup program including DLL/vsix files built by same msbuild session.

Modify Setup_Npgsql.nsi to set up setup version and assembly's version.
```
!define VER "2.2.0-rc2"
!define ASMVER "2.2.0.0"
```

Check #128 for the discussion of setup.

Prerequisites for build servers:
- Get NSIS 2.46 and install it. http://nsis.sourceforge.net/Download
- Get experienceui-1.3.1.exe and install it. http://nsis.sourceforge.net/ExperienceUI

WiX Toolkit's script *installer\NpgsqlSetup.wxs* is also included. It is incomplete for now.