[SPARK-8111] [SPARKR] SparkR shell should display Spark logo and version banner on startup.

spark version is taken from the environment variable SPARK_VERSION

Author: Alok  Singh <singhal@Aloks-MacBook-Pro.local>
Author: Alok  Singh <singhal@aloks-mbp.usca.ibm.com>

Closes #6944 from aloknsingh/aloknsingh_spark_jiras and squashes the following commits:

ed607bd [Alok  Singh] [SPARK-8111][SparkR] As per suggestion, 1) using the version from sparkContext rather than the Sys.env. 2) change "Welcome to SparkR!" to "Welcome to" followed by Spark logo and version
acd5b85 [Alok  Singh] fix the jira SPARK-8111 to add the spark version and logo. Currently spark version is taken from the environment variable SPARK_VERSION

R/pkg/inst/profile/shell.R

@@ -27,7 +27,21 @@
   sc <- SparkR::sparkR.init()
   assign("sc", sc, envir=.GlobalEnv)
   sqlContext <- SparkR::sparkRSQL.init(sc)
+  sparkVer <- SparkR:::callJMethod(sc, "version")
   assign("sqlContext", sqlContext, envir=.GlobalEnv)
-  cat("\n Welcome to SparkR!")
+  cat("\n Welcome to")
+  cat("\n")
+  cat("    ____              __", "\n")
+  cat("   / __/__  ___ _____/ /__", "\n")
+  cat("  _\\ \\/ _ \\/ _ `/ __/  '_/", "\n")
+  cat(" /___/ .__/\\_,_/_/ /_/\\_\\")
+  if (nchar(sparkVer) == 0) {
+    cat("\n")
+  } else {
+    cat("   version ", sparkVer, "\n") 
+  }
+  cat("    /_/", "\n")
+  cat("\n")
+
   cat("\n Spark context is available as sc, SQL context is available as sqlContext\n")
 }