[cmake|win32] allow webserver to be disabled on windows

[Rechi]

Description

The defines HAS_WEB_SERVER and HAS_WEB_INTERFACE are already defined if HAVE_LIBMICROHTTPD is defined. There is no need to generally set it for windows.
TestWebServer must only be compiled if the HTTPRequestHandlers are build.

How Has This Been Tested?

Compiled on Windows with disabled microhttpd.

Checklist:

• My code follows the Code guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the CONTRIBUTING document
• I have added tests to cover my change
• All new and existing tests passed

[fetzerch]

Thanks! When I started with cmake on windows, I found a few places with #pragma lib that might have become obsolete now.

[fetzerch]

jenkins build and merge