systemctl add command list-dependencies

systemctl list-dependencies lists all unit's dependecies and
recursively expands all subsidiary target units into a tree.

Primary purpose for this command is to show all units which are
enabled in specified target.

src/shared/util.c

@@ -5648,12 +5648,14 @@ const char *draw_special_char(DrawSpecialChar ch) {
                         [DRAW_TREE_VERT]          = "\342\224\202 ",            /* │  */
                         [DRAW_TREE_BRANCH]        = "\342\224\234\342\224\200", /* ├─ */
                         [DRAW_TREE_RIGHT]         = "\342\224\224\342\224\200", /* └─ */
+                        [DRAW_TREE_SPACE]         = "  ",                       /*    */
                         [DRAW_TRIANGULAR_BULLET]  = "\342\200\243 ",            /* ‣  */
                 },
                 /* ASCII fallback */ {
                         [DRAW_TREE_VERT]          = "| ",
                         [DRAW_TREE_BRANCH]        = "|-",
                         [DRAW_TREE_RIGHT]         = "`-",
+                        [DRAW_TREE_SPACE]         = "  ",
                         [DRAW_TRIANGULAR_BULLET]  = "> ",
                 }
         };

src/shared/util.h

@@ -555,6 +555,7 @@ typedef enum DrawSpecialChar {
         DRAW_TREE_VERT,
         DRAW_TREE_BRANCH,
         DRAW_TREE_RIGHT,
+        DRAW_TREE_SPACE,
         DRAW_TRIANGULAR_BULLET,
         _DRAW_SPECIAL_CHAR_MAX
 } DrawSpecialChar;