Refactor out note functions

* Add new note_edit() and note_view() helper functions. Use these
  instead of copy-pasted code in *_note_edit().

* Move all note-related functions (note_edit(), note_view(),
  note_erase()) to a new source file "note.c".

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/Makefile.am

@@ -19,6 +19,7 @@ calcurse_SOURCES = \
 	io.c \
 	keys.c \
 	llist.c \
+	note.c \
 	notify.c \
 	recur.c \
 	sigs.c \