added 'drop' signal that is triggered when a mouse button is released after a previous drag signal (and only then!), closes #173
cleaned up power traits a little
cleaned up power traits a bit more
Merge branch 'master' of github.com:MightyPirates/OpenComputers into MC1.7

Conflicts:
	src/main/scala/li/cil/oc/common/tileentity/traits/PowerAcceptor.scala
	src/main/scala/li/cil/oc/server/TickHandler.scala
Merge branch 'master' of github.com:MightyPirates/OpenComputers into MC1.7

Conflicts:
	src/main/scala/li/cil/oc/common/block/PowerConverter.scala
	src/main/scala/li/cil/oc/common/tileentity/traits/PowerAcceptor.scala
	src/main/scala/li/cil/oc/common/tileentity/traits/power/ThermalExpansion.scala
	src/main/scala/li/cil/oc/common/tileentity/traits/power/UniversalElectricity.scala