CometLogger improvements
🚀 Features

Save the offline experiment data in the same directory as the model's checkpoint directory
Use the experiment name in the directory name for the experiment
Fix the name property on the logger (this part is a bug more than a feature request)

Motivation / Pitch
Suppose I set up my logger and trainer like this:
import pytorch_lightning as pl

logger = pl.loggers.CometLogger(
    save_dir="/home/user/models",
    project_name="my_project",
    experiment_name="my_exp",
)
trainer = pl.Trainer(logger)
model = ...
trainer.fit(model)

If the id of my experiment was 123 then I'd have the offline experiment file at /home/users/models/123.zip. The rest of the data from that training run would be at /home/users/models/my_project/123/ . I think it would be nicer if the 123.zip file was at /home/users/models/my_project/123/123.zip.
For easier discoverability, it would be nice to have the experiment name as part of the name of the directory. So instead of /home/users/models/my_project/123/, the directory could be /home/users/models/my_project/my_exp/ or perhaps /home/users/models/my_project/my_exp_123/. Then one could find experiments by name.
If I check logger.name, I'll get "my_project" instead of "my_exp". The getter should be return str(self.experiment.get_name()) instead of the current return str(self.experiment.project_name).

Cons

Having all of the offline experiment zip files in the same directory probably makes it easier to upload them to the Comet website. I don't think this would be very hard with the zip files in each experiment's own directory, but it might take a slightly more complicated bash command.
I don't think we can implement 1. unless we remove the experiment ID from the directory name; we have to pass the save directory when creating the offline experiment, but at that point no ID has been assigned yet. If 2. is also done and we just use the experiment name, without the id, then 1. would be easy to implement. If we want things to be robust to multiple experiments with the same name, we could add _{i} to the name where i is 0 by default and takes on the smallest unused integer value if there are already directories with the same experiment name (this has the added benefit of making it easy to tell what order I ran the experiments in, so I could, e.g., find the most recent run of an experiment with a certain name).

Implementation
I'm happy to implement these features if a PR would be accepted.