Fix Issue#147

The `ExporterTest` class was overwriting XML files in the `src/test/resources/testOutput` directory. So that's why they appeared as modified under git status after running the tests. I introduced a new class `TemporaryFolder` that mimics JUnit rule with the same name. This allows to export components to a temporary folder and make sure that the folder will be deleted after the test run.

* Wrote or re-wrote unit tests (Y/N): Y
* Ran entire suite of unit tests successfully (Y/N): Y
* Verified bug fix with the described replication steps or verified the implementation meets the requirement cited (Y/N): Y
* Code coverage requirements satisfied (new code=80%, changed code=at least as high as existing) (Y/N): Y
* Code review date and attendees: Code review by pull request

There is no potential impact on other areas of the code since the modification was done in unit tests.