data_push should have a more clear message when file does not exist

[hafen]

The error message for data_push when a file doesn't exist isn't very clear. I get the same error when a file doesn't exist as when I try to push a directory (see #2). The error is:

ValueError: local_path must be a file.

It would be nice if the error message indicated that the file does not exist.

[pcstout]

@hafen Is this better?

>>> p.data_add('/tmp/does_not_exist.csv')
ValueError: Please specify a remote URI or a local file or folder path that exists.

>>> p.data_pull('/tmp/does_not_exist.csv')
kitools.exceptions.KiProjectResourceNotFoundError: No project resource found matching: /tmp/does_not_exist.csv

>>> p.data_push('/tmp/does_not_exist.csv')
kitools.exceptions.KiProjectResourceNotFoundError: No project resource found matching: /tmp/does_not_exist.csv

[hafen]

Yes this is better.

For data_push() and data_pull(), what do you think of adding two hints:

• Use data_list() to look at the remote URI or name for valid resources.
• If the resource you want to push/pull is not in this list, add it with data_add().