Use nuget -restore functionality

- Download nuget.exe from its official home
- Remove beta nuget.exe from monad-ext
- Specify dependencies in packages.config and use nuget.exe -restore
- Add prepare dependency to package libraries
- No more manual prepare step
- Update .gitignore

.gitignore

@@ -1,12 +1,11 @@
 .idea
 .config/
-.nuget\\packages\\/
+.local/
 CMakeCache.txt
 CMakeFiles/
 Makefile
 !scripts/Makefile
 cmake_install.cmake
-externals
 scripts/xunittests.xml
-/scripts/powershell.inc
+scripts/powershell.inc
 .bash_history