Added particle effect on found items.
hexagon, improved startup speed

Instead of having an Audio drip sound in each HexagonItem we have a
global one in the main activity code. This increases the startup speed.
menu, added click feedback

On older system an activity maybe long to start and we had no visual
feedback that the click was taken in account. In this patch we launch
the activity asynchronously and we put our particle star effect on the
activity icon.
Initial implementation of the memory activity
memory, simplified code, added a matchcode.

The match code is use to check 2 cards are the same instead
of checking the image name. In some cases cards may have different
images and match (math memory for example).
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/activities/memory/CardItem.qml
	src/activities/memory/Memory.qml
	src/activities/memory/memory.js