enable multi-apps for SSC

Podhorszki, Norbertrequested to merge
github/fork/shevateng0/ssc-multi-app into master

Created by: shevateng0

Need the ssc engine to run multiple applications (>2). However, the original program can only communicate between the intra communicators of two applications. I add some codes to allow the commnunication among the intra communicators of multiple applications.

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