E1S7: rework WML event to use CLEAR_CAVE_SHROUD and [filter_condition]
E1S7: rework touchplate events

 * Refresh terrain and shroud after the event notification
 * Use HIGHLIGHT_GOAL in the second touchplate event and clear a larger
   shroud region
E1S7: trigger easter-egg event on a larger range along the X axis

This range corresponds to the locations from which Elynia may see the
right edge of the map according to her movetype and MP.
E1S7: Don't scroll the map for a one-liner sight event