feat: exclude some files from uploading

[mdreizin]

It would be nice to exclude files from uploading using glob patterns or just path to file:

files:
    default:
        push:
            exclude:
            - lang/foo/*.json
    "translations/**/*.json":
        push:
            type: "json"
            # or use `exclude` here
            exclude:
            - lang/foo/*.json

If have lang/foo/en-US.json (or other files under lang/foo/*) then they will excluded from uploading:

1. smartling.yml is used:

smartling-cli files push

2. override via arguments:

smartling-cli files push --exclude=lang/foo/*.json

EXAMPLE:

https://github.com/Fitbit/smartling/blob/master/README.md (please see Files.PathExclude option)
https://github.com/Fitbit/smartling/blob/master/model/project_resource.go#L77
https://github.com/Fitbit/smartling/blob/master/model/project_resource_test.go#L39