Issue 156 ReleaseScraper tests

This PR addresses Issue #156

I implemented every manual test for the ReleaseScraper except the ones with the `-d` flag as we are arguably already testing the functionality with the creation and use of `self.temp_dir` in the tests.

So far, I only tested the correctness of `scraper.target`, but I noticed that when specifying `-v latest`, the name of the file to be downloaded, differs from `scraper.target`. I tried to account for that with the file names.

One type down, three more to go! :)