Implementation of trigger cell neighbors

[jbsauvan]

Issue #4

• Update geometry interface to retrieve trigger cells neighbors (getNeighborsFromTriggerCell(unsigned), returns an unordered set of neighbor ids)
• Store in maps the wafer neighbors and trigger cell neighbors within wafers, and compute the trigger cell neighbor ids from these maps
• Add consistency check of the trigger cell neighbor in the test module and update geometry tree with neighbor information