Ncurses UI for `cornerstone`: `cornerstone --ui=ncurses`

• Draw status bar (at the top of terminal): CORNERSTONE, To-do items list, State: opened with alignment and coloring.
• Draw the buttons bar (F1, F5, F6, F7, F10).
• Implement entering the UI: cornerstone --ui=ncurses (UIs should be stored at /usr/local/share/cornerstone/ui/; for the UI in development: subdirectory ncurses).
• Implement exiting from the UI using the F10 key.
• Merge the branch into the master, create tag, publish tarball and port for 0.3