Removed the md5 library, obsoleted by PolarSSL.

Fixes #1130.
Added PolarSSL dependency to Bindings.
Changed include folders to work for Bindings, too.
CMake: Added polarssl include dir as non-system.
Fixed a silly path error in #include.
Merge pull request #1132 from mc-server/RemoveMD5

Removed the md5 library, obsoleted by PolarSSL.