[Scenario] Add slider below ticks/pan controls

Add a two-ended slider bar below pan controls,
time ticks in timeline/scenario views; this
will later be used to control pan and zoom
more quickly, in order to support resolution
of nasa/MCT-Plugins#128.
[Scenario] Colorize composite pan/zoom slider
[Scenario] Update timeline zoom from composite control
[Scenario] Update timeline pan from composite control
[Scenario] Stop timeline pan animation

Fix a bug in timeline pan animation which
permitted the timer to execute indefinitely
(due to reductions in speed of pan, target
center time is never quite reached, so
condition termination of timer on reduction
of animation speed to less-than-a-pixel.)
[Scenario] Update composite pan/zoom sliders

Update position of composite pan/zoom sliders
when start and end times are changed elsewhere
(e.g. due to panning.)
[Scenario] Add connecting lines above pan/zoom control

Add connecting lines above composite pan/zoom
control in timeline views to visually correlate
the position of those sliders with the time
span shown in tick marks above.
[Scenario] Make edge width of MultiSlider gettable

Provide getter for edge width (pixels not
allocated to the slideable portion of the
component) of Multi-Slider; this will allow
other components (connecting lines) to
align themselves visually.
[Scenario] Align connecting lines

Account for internal positioning of
MultiSlider when drawing connecting lines
to illustrate its relationship to the
visible timescale.
[Scenario] Decrease connector height

Decrease vertical space consumption of lines
which connect multi-slider to tick marks in the
time line view.
[Scenario] Tweak color, position of pan/zoom
[Scenario] Revise appearance of pan/zoom control

Revise appearance of timeline composite pan/zoom
control (more rounded, color tweaks); additionally,
fixes some issues relating to bounds that caused
component to appear/interact incorrectly when
partially invisible.
Merge pull request #144 from VWoeltjen/mctPlugins128

[Scenario] Add composite pan/zoom control