Feature #138 top level mobility model

After massive problems with the original branch and merge request, here is a new one. There won't be unit tests in this MR.

configurations/VoluntaryHelperMovementTest.txt

+# Define 2 different node groups
+Scenario.nrofHostGroups = 2
+
+# Common settings for all groups
+Group.movementModel = VoluntaryHelperMovement
+Group.router = EpidemicRouter
+Group.bufferSize = 5M
+Group.waitTime = 0, 120
+# All nodes have the bluetooth interface
+Group.nrofInterfaces = 1
+Group.interface1 = btInterface
+# Walking speeds
+Group.speed = 0.5, 1.5
+# Message TTL of 300 minutes (5 hours)
+Group.msgTtl = 300
+Group.nrofHosts = 100
+
+# group1 (pedestrians) specific settings
+Group1.groupID = p
+Group1.isLocalHelper = true
+
+# group2 (cars) specific settings
+Group2.groupID = c
+Group2.speed = 10, 30
+
+## Message creation parameters
+# How many event generators
+Events.nrof = 2
+# Class of the first event generator
+Events1.class = MessageEventGenerator
+# (following settings are specific for the MessageEventGenerator class)
+# Creation interval in seconds (one new message every 25 to 35 seconds)
+Events1.interval = 25,35
+# Message sizes (500kB - 1MB)
+Events1.size = 500k,1M
+# range of message source/destination addresses
+Events1.hosts = 0,199
+# Message ID prefix
+Events1.prefix = M
+
+#Settings for the disaster and hospital events
+# max number of external events to preload (default = 500)
+Events2.nrofPreload = 3
+# path to external events file
+Events2.filePath = ee/test/VHMTestEvents.json