PTFM-7307: Basic support for job tags and properties

@kislyuk or @psung, care to review?  See the commit message for an overview of the changes.

I should note, however, that there is a breaking change, removing the ability to say `dx run appname --tag apptag` to be equivalent to `dx run appname/apptag`.  I imagine, however, that few people (if any) have used the previous syntax and would find the second method for specifying an app's tag or version to be more succinct and usable.  I also think the new usage of `--tag` to be more natural (akin to `dx new record --tag ...`).  I also reordered some kwargs, but this should only be a problem if they are called positionally (which they shouldn't be).