Added helper methods for spring

[garethahealy]

Added helper methods to the builder to make it easier for the end user when configuring dozer.

CC @orange-buffalo ; any views?

[orange-buffalo]

@garethahealy, looks good to me, just one thought here. I would keep builder methods which accept single object instead of deprecating them. Imo, code like this:

    ...
    .withCustomConverter(MyConverterBuilder.create()
            .withThis(..)
            .withThat(..)
            .build())
    .withCustomConverter(AnotherConverter.ofSomething(..))
    .withCustomConverter(new SimpleCoverter())
    ...

is more expressive than

    ...
    .withCustomConverters(MyConverterBuilder.create()
            .withThis(..)
            .withThat(..)
            .build(),
            AnotherConverter.ofSomething(..),
            new SimpleCoverter())
    ...

We could call withCustomConverters with single argument multiple times, but then it looses its semantics.
Of course, this is a matter of personal preferences, do not insist that it is the only and the best way :)

[garethahealy]

@orange-buffalo ; removed the deprecated as requested. I am easy either way, so left them.

[orange-buffalo]

@garethahealy thanks!