Part 6.0 - "Using Constructor Injection".

Set triangle type to "Equilateral" using constructor injection.

Add constructor-arg for type parameter in spring.xml.
Add a no-argument constructor, two one-argument constructors (one for
type and one for height) and a two-argument constructor (type and
height) to Triangle.java.

Signed-off-by: Bob Piper <bob.piper1953@virginmedia.com>