refactor tree_move() into src/move.c, change config (!), change testcase

Due to lots of cases which were added and added to tree_move(), the function
was not really easy to understand. For this refactoring, I wrote tree_move()
from scratch, thinking about (hopefully) all cases. The testsuite still passes.

The move command also has different parameters now. Instead of the hard to
understand 'before v' stuff, we use 'move [left|right|up|down]'.

src/con.c

@@ -230,6 +230,24 @@ Con *con_get_workspace(Con *con) {
     return result;
 }
 
+Con *con_parent_with_orientation(Con *con, orientation_t orientation) {
+    DLOG("Searching for parent of Con %p with orientation %d\n", con, orientation);
+    Con *parent = con->parent;
+    if (parent->type == CT_FLOATING_CON)
+        return NULL;
+    while (con_orientation(parent) != orientation) {
+        DLOG("Need to go one level further up\n");
+        parent = parent->parent;
+        /* Abort when we reach a floating con */
+        if (parent && parent->type == CT_FLOATING_CON)
+            parent = NULL;
+        if (parent == NULL)
+            break;
+    }
+    DLOG("Result: %p\n", parent);
+    return parent;
+}
+
 /*
  * helper data structure for the breadth-first-search in
  * con_get_fullscreen_con()
@@ -742,15 +760,44 @@ void con_set_layout(Con *con, int layout) {
 }
 
 static void con_on_remove_child(Con *con) {
+    DLOG("on_remove_child\n");
+
     /* Nothing to do for workspaces */
-    if (con->type == CT_WORKSPACE)
+    if (con->type == CT_WORKSPACE || con->type == CT_OUTPUT || con->type == CT_ROOT) {
+        DLOG("not handling, type = %d\n", con->type);
         return;
+    }
 
     /* TODO: check if this container would swallow any other client and
      * don’t close it automatically. */
-    DLOG("on_remove_child\n");
-    if (con_num_children(con) == 0) {
+    int children = con_num_children(con);
+    if (children == 0) {
         DLOG("Container empty, closing\n");
         tree_close(con, false, false);
+        return;
+    }
+
+    /* If we did not close the container, check if we have only a single child left */
+    if (children == 1) {
+        Con *child = TAILQ_FIRST(&(con->nodes_head));
+        Con *parent = con->parent;
+        DLOG("Container has only one child, replacing con %p with child %p\n", con, child);
+
+        /* TODO: refactor it into con_swap */
+        TAILQ_REPLACE(&(parent->nodes_head), con, child, nodes);
+        TAILQ_REPLACE(&(parent->focus_head), con, child, focused);
+        if (focused == con)
+            focused = child;
+        child->parent = parent;
+        child->percent = 0.0;
+        con_fix_percent(parent);
+
+        con->parent = NULL;
+        x_con_kill(con);
+        free(con->name);
+        TAILQ_REMOVE(&all_cons, con, all_cons);
+        free(con);
+
+        return;
     }
 }