Refined Visual Studio 2013 Builds

* Project file factored into non-redundant properties files for ease of maintenance.
* Restructured file locations to ensure no conflict when building multiple configurations.
* Visual Studio UI extended to present options for building with `Testnet` and/or `LevelDB`.
* Build info added to output. Configuration parameters refined.
* Commented in support for non-portable stealth database.
* Fixed a number of 64bit numeric inconsistencies (although some remain).
* Removed use of `_WINDOWS` in favor of `_WIN32` (general windows) and `_MSC_VER` (compiler).
* Cosmetic fixes and fixes for some trivial compiler warnings.
* One line of code **session.cpp:115** disabled in `_MSC_VER` builds (work in progress).
* NuGet dependencies are not yet available in `v120` compilation so may fail at run time.
* Until they are updated, NuGet dependencies require updated targets to link, see:
    * [curl-nuget-targets](https://github.com/evoskuil/curl-nuget-targets)
    * [libssh2-nuget-targets](https://github.com/evoskuil/libssh2-nuget-targets)
    * [openssl-nuget-targets](https://github.com/evoskuil/openssl-nuget-targets)
    * [zlib-nuget-targets](https://github.com/evoskuil/zlib-nuget-targets)