cmake conversion #3

The "doc" and "po" folder are actually empty, as a result I've left them commented in the CMakeLists.txt.

I've added some options for the user to pass where It was marked as FIXME in src/libtdeldap.cpp.

As expected, further work was needed.

The Heimdal C API is used in the master branch; therefore, for Kerberos should be preferred Heimdal and we need to make sure that Kerberos is Heimdal.
To prevent portability issue, I added the detection whether the compiler supports the option -fpermissive.
The library version was 1.0.0 for Automake build, so I added the same version for CMake build.
Because there are big differences between the master branch and r14.0.x, there was a need for further work with the backport for the r14.0.x branch.

Please test building on your system before I'll go ahead to merge.

Although libtdeldap is a library, in the libtdeldap.h header, no class is marked as exported. And some classes with the Private note are used in other applications – such as LDAPPamConfig in kcmldap.

This is not compatible with hidden visibility. That's why we need more work to fix it.

Thanks to commit 32c6b4398e is now possible to build libtdeldap with gcc hidden visibility.