Fixed emacs lisp compilation

Fixed a compile error, caused by `lisp/ledger-context.el` not being present in the `CMAKE_CURRENT_BINARY_DIR` during compile time. Bug presumably introduced with 3105f13a7be56ea7b6e210b98742b4e1f9694e3f
Additionally, moved installation destination of emacs lisp files into subdirectory of site-lisp.