Package Manager UI Improvements

### Improvements

This pull request addresses 6 issues with the package manager UI in Dynamo:

##### MAGN-4778: Object Reference not set to an instance of an object – erroneous error message when Package Manager invoked in standalone mode

This is fixed by detecting when an OAuth authenticator is present - `PackageManagerClient.HasAuthenticator ` is now called in the `CanIssueCommand` method for any `Command` that requires an authenticator (Upvote, Downvote, Deprecate, NewPackage, etc). 

##### MAGN-4777:  Publish Package button stays greyed out after all requirements are met

The `RaiseCanExecuteChanged` event has to be emitted for the `SubmitCommand` in `PublishPackageViewModel.`  This usually would never be required as before all packages already had a file.

##### MAGN-4735:  Use TT GBS files as test data

I've obtained and have tested the files extensively using the staging server.  I published multiple versions as well.  Things look pretty solid and the files run.

##### MAGN-4781:  Package Manager - Add File dialog should allow multiple selection

This is a simple switch in the `OpenFileDialog` in `PublishPackageViewModel.`

##### MAGN-4782:  Package Manager - need to be able to add dyn, rfa and rvt sample content to package

Again, I modified the `OpenFileDialog` to add any file.  `PackageUploadBuilder` was modified to support this change as well.  Notably, it needed to be modified to properly categorize xml files that should be in the bin directory (e.g. XML documentation and DynamoCustomization files)

##### MAGN-4780: Package Manager - Add File dialog should remember the last location used

Again, a simple modification to `OpenFileDialog` in `PublishPackageViewModel.`


### Reviewers

@ikeough