Migrating trim and finders_table tests to unit_tests

I've moved `run_trim_test.py` and `test_build_finders_table.py` to `tests/unit_tests`. I've updated their import statments, and the import statements of some of the functions they call, to be of the form `mtpipeline.[foldername].[filename]`. 

I've moved the `ephem` folder from `MTpipeline/ephem` to `MTpipeline/mtpipeline/ephem`, so that it is built as a submodule of the `mtpipeline` module. I've also removed a duplicate `test_jpl2db.py` that was sitting in `ephem` (there is a `test_jpl2db.py` in the legacy tests, although its import statement needs correcting).

If this request is approved, we can close [Ticket#109](https://github.com/STScI-Citizen-Science/MTPipeline/issues/109).
There is a small but subtle issue here. If the `yaml.load` command fails in the `except` statement we will get an `IOError` that says `template_settings.yaml` is missing. This is slightly misleading because the issue is actually that we're missing `settings.yaml` _and_ `template_settings.yaml`. 

So, I think what we want to do is 
1. Try `settings.yaml`
2. If we don't find that we should try `template_settings.yaml`
3. If we don't find either we should then raise a custom error massage.

I think we should use a nested try/except pattern like this:

```python
try:
    settings = yaml.load(open(os.path.join(settings_path,'settings.yaml')))
except IOError:
    try:
        settings = yaml.load(open(os.path.join(settings_path,'template_settings.yaml')))
    except IOError:
        raise IOError("Looked for a setting.yaml and then a template_settings.yaml file at the package root level and found neither.")
```

Here is a [SO question[(http://stackoverflow.com/questions/17015230/are-nested-try-except-blocks-in-python-a-good-programming-practice) giving some background and explaining the [EAPF](https://docs.python.org/3/glossary.html#term-eafp) design principle in Python.