Add Npc 375 for annual easter events. (3 Eggs on the Ground)
Add recolored eggshell heads.
Optimized eggshell hats:

 * Delete png/xml files of recolored eggshells.
 * Made original eggshell hat dyeable (reduce number of shades + desaturate)
 * Add dye string for current eggshell hat (give back its slight blue tint)
 * Add dye strings for the 6 easter 2013 eggshell hats
 * Fix incorrect IDs of orange/dark eggshell hats
Merge branch 'easter'

Conflicts:
	items.xml
055-1: Fixed Fringe layer, added Ground2.
056-1: Fixed Fringe layer, renamed Road to Ground2, fixed some incomplete treetrunks
Collision fixes for 055-1 and 056-1.
008-1: Fixed Fringe Layer, added Ground2.
Adapt the item description of the colored Easter eggs.

Since the event where you got a prize for collecting all of them isn't active anymore,
the description was misleading.
Add a particle effect that can be used when the player receives some object.
Add new id for invisible npcs, make old id not selectable as suggested by 4144.

Previously id 127 was used for both regular npcs with an invisible sprite
and npcs used for e.g. spell effects, which shouldn't be selectable, but were.