If given a directory, search that directory for files

We have a number of ipa / apk and dsym files in our workspace, so we need finer control over what files are sent to testflight.

This change enables a user to input a directory into the text fields, which then are used to search for the relevant files.

If the inputs are empty, the workspace is searched. If the inputs are actual files, that file is used. If a non-existent file (or directory) is specified, then an exception is thrown.  Therefore the current behavior should be the same.