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]'.

include/tree.h

@@ -65,13 +65,6 @@ void tree_close_con();
  */
 void tree_next(char way, orientation_t orientation);
 
-/**
- * Moves the current container in the given way (next/previous) and given
- * orientation (horizontal/vertical).
- *
- */
-void tree_move(char way, orientation_t orientation);
-
 /**
  * Closes the given container including all children
  *