Fix time accounting on msp430 Series 1 and Series 2 MCU based platforms.

The problem with the current version of the code was that the condition at the end of the do...while loop at Timer A1 interrupt:
 while((TACCR1 - TAR) > INTERVAL);
evaluates to false whenever TACCR1 == TAR.
Not incrementing TACCR1 in this case leads to Timer A1 interrupt not being called for 2 seconds, until TAR counter reaches TACCR1 again after an overflow.

The patch avoids this problem by changing the condition of the loop, and using CLOCK_LT macro to compare between time values.

The patch also attempts to fix another problem: a read of TAR register while it is being updated may return a lower value than the actual contents. To avoid that, the "read twice and compare results" idiom should be used. As the TAR register is updated by the actual hardware, it is of no importance whether it is read with interrupts disabled or enabled; the problem can occur in both contexts.
[cooja] plugins/analyzers: Added PacketAnalyzer for 6lowpan fragmentation header
[cooja] plugins/Visualizer: Fix: Always highlight selected motes.

Motes were highlighted only by the UDGMVisualizerSkin before.
Now highlighting moved from individual VisualizerSkin to Visualizer.

A selected mote is highlighted with a blue circle
and a semi-transparent gray overlay.
[cooja] plugins/Visualizer: Enable multi-mote deletion in mote menu
[cooja] plugins/Visualizer: Fixed node selection in Delete menu handling

Previously if multiple motes were selected
and the context menu of a non-selected mote
was used to delete, not the clicked mote
but the other selected ones were removed.

This behavior is fixed so that if another
mote is clicked only this is deleted.
[cooja] plugins/Visualizer: Implemented multi-mode behavior of delete mote menu for move, too

Note that this does not yet implement the correct behavior of beginMoveReques()
[cooja] plugins/Visualizer: Group mote placement modifications together (move, delete)
[cooja] plugins/Visualizer: Mouse release always terminates previous action
and reses actions state and cursor appearance

Also renamed UNKNOWN state to NONE as it is a more adequate name for the new behavior
[cooja] plugins/Visualizer: Partly implement behavior of beginMoveRequest to fit new mote movement handling
[cooja] plugins/Visualizer: Key control: Allow to abort actions with ESCAPE key and delete motes using DELETE key
[cooja] plugins/Visualizer: Deselect motes when removing

This also fixes visualization issues such as
remaining transmission range underlays for removed motes
[cooja] skins/TrafficVisualizerSkin: Added @Override annotations and added some final modifiers
[cooja] skins/TrafficVisualizerSkin: Indicate sent but unreceived messages by a red double circle around mote
[cooja] skins/TrafficVisualizerSkin: Use LinkedList instead of ArrayList to increase add and remove performance
[cooja] skins/TrafficVisualizerSkin: Removed unnecessary 'historyCopy'
[cooja] skins/TrafficVisualizerSkin: Reduce array copy and iteration overhead
[cooja] skins/TrafficVisualizerSkin: Age handling moved to RadioConnectionArrow class which also got some lines of function documentation
[cooja] skins/TrafficVisualizerSkin: Use alpha value to fade out arrow color an potentially allow to configure colors
[cooja] plugins/sinks/TrafficVisualizerSkin: Synchronized to avoid ConcurrentModificationExcpetions
[cooja] plugins/analyzers: Indention and whitespace cleanups