[SPARK-10979][SPARKR] Sparkrmerge: Add merge to DataFrame with R signature

Add merge function to DataFrame, which supports R signature.
https://stat.ethz.ch/R-manual/R-devel/library/base/html/merge.html

Author: Narine Kokhlikyan <narine.kokhlikyan@gmail.com>

Closes #9012 from NarineK/sparkrmerge.