PropertyName should resolve to the last token

[gmarz]

Since dots are no longer allowed in field names since ES 2.0, it makes sense for PropertyName to always resolve to the last token.

For instance

 .Fields(fs => fs
    .String(s => s
        .Name(p => p.Foo.Suffix("raw"))
    )
)

or

 .Fields(fs => fs
    .String(s => s
        .Name("foo.raw")
    )
)

should resolve to just raw.

Relates #1707