Add mono build script (#70) with Travis CI and add config file

This add limited support for Travis CI. At the moment, we only build
the R Provider and do not run the tests. This is future work - we need
to figure out how to install R on Travis first.

The commit also includes some work on adding configuration file
(which is completed in a later commit).
Concurrency fixes

Protect all access to RDotNet through RInterop using a lock on
RInit.engine. IDE stability issues, apparent parsing errors, and system
access errors are resolved by ensuring that the R environment through
RDotNet is accessed in a thread-safe manner.
TODO #73
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