Draw line of previous bus location when refreshing

[qtrandev]

From @qtrandev on May 12, 2015 19:29

Requested by Cristina. When doing a refresh, instead of moving the marker, a line should be drawn from the previous location so the user can see the path history.

Copied from original issue: qtrandev#28

[qtrandev]

See the history of commits in qtrandev#28
Note that currently, only the GPS tracker shows history locations. History was attempted but disabled for other icons since the map became too crowded and the history icons seems to slow down the map.
Add comment here if there's anything else we should do on this.