Compile CalcManager project with or without precompiled headers (#436)

Fixes #324 .

Description of the changes:
In an effort to support other compilers (#109), this change reworks how precompiled headers are handled. For toolchains where precompiled headers are not used, there is unnecessary compilation cost because each source file explicity includes the pch, meaning all system headers in the pch were recompiled for each translation unit. This change modifies the project's files so that each translation unit includes a minimal set of dependent headers. For MSVC users, the precompiled headers option is still enabled and the precompiled header is added to each translation unit using the compiler's Forced Includes option. The end result is that MSVC users still see the same build times, but other toolchains are free to use or not use precompiled headers.

Risks introduced
Given that our CI build uses MSVC, this change introduces the risk that a system header is added to the pch and the CalcManager project builds correctly, but builds could be broken for other toolsets that don't use pch. We know we want to add support for Clang in our CI build (#211). It seems reasonable to also compile without precompiled headers there so that we can regression test this setup.

How changes were validated:
Rebuild CalcManager project. Compile time: ~4.5s.
Disable precompiled headers, keeping explicit include for pch in each source file. Compile time: ~13s.
Remove explicit pch inclusion and add the appropriate headers to each translation unit to allow the project to compile. Compile time: ~8s.
Re-enable pch and include it using the Forced Includes compiler option. MSVC compile time: ~4.5s.
Minor changes
Delete 'targetver.h'. I found this while looking around for system headers in the project. It's unused and unreferenced so let's remove it.

src/CalcManager/pch.h

@@ -3,27 +3,20 @@
 
 #pragma once
 
-#ifndef WIN32_LEAN_AND_MEAN
-#define WIN32_LEAN_AND_MEAN
-#endif
+// The CalcManager project should be able to be compiled with or without a precompiled header
+// in - order to support other toolchains besides MSVC. When adding new system headers, make sure
+// that the relevant source file includes all headers it needs, but then also add the system headers
+// here so that MSVC users see the performance benefit.
 
-// Windows headers define min/max macros.
-// Disable it for project code.
-#define NOMINMAX
-
-#include <assert.h>
-#include <windows.h>
-#include <winerror.h>
-#include <sstream>
-#include <iostream>
-#include <iterator>
-#include <string>
-#include <memory>
-#include <vector>
-#include <limits>
-#include <list>
-#include <regex>
-#include <unordered_map>
-#include <intsafe.h>
+#include <algorithm>
 #include <array>
+#include <cassert>
+#include <intsafe.h>
+#include <list>
 #include <ppltasks.h>
+#include <regex>
+#include <sstream>
+#include <string>
+#include <unordered_map>
+#include <vector>
+#include <winerror.h>