[SPARK-1696][MLLIB] use alpha in dense dspr

It doesn't affect existing code because only `alpha = 1.0` is used in the code.

Author: Xiangrui Meng <meng@databricks.com>

Closes #778 from mengxr/mllib-dspr-fix and squashes the following commits:

a37402e [Xiangrui Meng] use alpha in dense dspr
[Typo] propertes -> properties

Author: andrewor14 <andrewor14@gmail.com>

Closes #780 from andrewor14/submit-typo and squashes the following commits:

e70e057 [andrewor14] propertes -> properties
[SPARK-1826] fix the head notation of package object dsl

Author: wangfei <scnbwf@yeah.net>

Closes #765 from scwf/dslfix and squashes the following commits:

d2d1a9d [wangfei] Update package.scala
66ff53b [wangfei] fix the head notation of package object dsl