Cherry-picked changes from `SFX-8` branch that should have been commited to `master`.

- Made adjustments to the Duration class so that javafx.util.Duration instances are consistently wrapped within scalafx.util.Duration instances.

- Added an auxiliary constructor to the Duration class to facilitate the above changes, in addition to providing the user with another way to create a scalafx.util.Duration instance (by using the auxiliary constructor directly)

- Minor updates to Scaladoc in the Duration class.

- One minor update made to DurationSpec test class to match the above changes.

- Made a minor update to the 'time' method to wrap the retrieved javafx.util.Duration object with scalafx.util.Duration.
Cherry-picked changes from `SFX-8` branch that should have been committed to `master`.

- Updated some lines that were forgotten in the initial commit for this patch.
- Very minor Scaladoc update (to avoid repetition of the word 'duration' in a single line of Scaladoc)
Cherry picked fix from SFX-8 branch.

Correct regression introduced in previous commit.
Dividing Duration by Duration should have no unit. Should be simple double, as the comment above the method indicates.
First step in renaming `Issue108` package to `issue108`.
Second step in renaming `Issue108` package to `issue108`.
Minimize dependencies - manual back-port from SFX-8 branch.
Cherry-picked commits from SFX-8 branch.

1) Added missing constructors to the EventType class. This involved some special measures to prevent compilation errors, which have been explained in code comments.

2) Removed usage of named 'delegate' parameter, as the same kind of disambiguation can be more elegantly achieved by specifying [T] when creating a new EventType.