[SPARK-2434][MLlib]: Warning messages that point users to original MLlib implementations added to Examples

[SPARK-2434][MLlib]: Warning messages that refer users to the original MLlib implementations of some popular example machine learning algorithms added both in the comments and the code. The following examples have been modified:
Scala:
* LocalALS
* LocalFileLR
* LocalKMeans
* LocalLP
* SparkALS
* SparkHdfsLR
* SparkKMeans
* SparkLR
Python:
 * kmeans.py
 * als.py
 * logistic_regression.py
Usually in Scala doc, we should use `[[org.apache.spark.mllib.ALS]]` in order to create a link in the generated html doc. With `[[...]]`, it is easy to add the period. You can also try to avoid having the classname at the end of the sentence.