Also populate single overlay inputs

We lean on the overlay service to obtain the active overlay.
FillDataValues: Use overlay input

Now that active input preprocessor populates overlays, let's use it.
Remove dependence on OptionsService and ImageDisplay

ActiveImagePreprocessor now handles Position, Dataset, and
ChannelCollection inputs, filling with default values if a single input
is needed. Note the TODO as preprocessing a ChannelColleciton input
should likely be done elsewhere but unsure where.

FillDataValues: Now longer relies on the OptionsService to get a color
for filling with. It also no longer relies on ImageDisplay. Instead it
takes, a ChannelCollection, Dataset, and Position.

Services: The Display and Overlay Services (Interfaces and default
implementations) were changed to accommodate the need to access the
active dataset and active position. Largely a suggestion but I expect
to use the methods widely in many other plugins.
Merge pull request #15 from jaywarrick/overlay-autofill

Overlay autofill