add tutorial and doc targets to cmake's all build

This way one can use -DWITH_TUTORIALS=1 and -DWITH_DOCS=1
to build the tutorials and docs and doesn't need to run extra
make commands.

Also this fixes the minor issue that `make install`
at the moment installs all tutorial *sources* with -DWITH_TUTORIALS=1
but nothing else if `make tutorials` wasn't called before that.