Run tests on "real" data

[vineetbansal]

Note: This should be tackled once PRs 28 and 29 are merged in.

We have the ability of download "real" data files using the wbi.data.ondemand.get_file() function. We should use this to:

1. Add the real sCMOS..dat file in our shared wbi_data dropbox folder (make a new subfolder to hold all the files from our currently used /bs folder). (Edit: I've now uploaded the scMOS..dat file up there).
2. The first invocation of get_file() should take a very long time. Subsequent calls will be quick. To avoid the initial cost of downloading (since you already have the file somewhere), step inside the get_file() function and see where pooch is trying to download the file (and with what name), and move your file there (make a soft link to that file from other locations if you still want regular access to it for other scripts etc).
3. Write a simple test for the flash finder against the real sCMOS..dat file, in a separate subfolder long_running_tests in the tests/ directory. The file should be obtained using get_file.
4. The return value of flash_finder should be inspected to see if we're detecting flashes at the correct time locations (3 separate flashes at specific timestamps).
5. These expensive tests should not be executed by default, but only explicitly on the command line. pytest.ini might need to be modified to make sure this is the case.
6. Submit a PR as soon as this is done without waiting to write more/better tests.

[vineetbansal]

Thanks!