Java examples included in 'mllib-linear-methods.md' file.

Standalone application examples are added to 'mllib-linear-methods.md' file written in Java.
This commit is related to the issue [Add full Java Examples in MLlib docs](https://issues.apache.org/jira/browse/SPARK-1945).
Also I changed the name of the sigmoid function from 'logit' to 'f'. This is because the logit function
is the inverse of sigmoid.

Thanks,
Michael
pom is specific to maven. we also support sbt for build. It should be sufficient to say "include spark-mllib` as dependencies. spark-mllib depends on spark-core so it is not necessary to include spark-core explicitly. Also, better not mention the scala version since then we need to update it if we upgrade to scala 2.11.