deauth queue when user logs out (#397), restart threads if they fail (#380)

[redshiftzero]

Description

Fixes #397
Fixes #380

Test Plan

In a single run of the client:

1. Log in
2. Ensure you can download a file (must be a file not a message)
3. Log out
4. Ensure that you cannot download a file (there isn't good user messaging in the UI - see my comment here)
5. Log back in
6. Ensure you can download the file now

Checklist

If these changes modify code paths involving cryptography, the opening of files in VMs, network (via the RPC service) traffic, or fine tuning of the graphical user interface, Qubes testing is required. Please check as applicable:

• I have tested these changes in Qubes
• I do not have a Qubes OS workstation (the reviewer will need to test these changes in Qubes)

[sssoleileraaa]

I still need to review the code, but I followed the test plan and everything worked as described.

I think this PR should also include removing the "Downloading file" message. It's pretty misleading since that's exactly what it is not doing. I read your comment about catching ApiInaccessibleErrors and setting the UI message there, however I imagine we will want to check if the user is offline before creating and making calls from DownloadJobs?

For now it might make sense to check whether or not the application is running in offline mode and returning a custom message for when they click on the Download link. Otherwise they will see this:

[redshiftzero]

added a commit to implement the behavior from the user's perspective described in #379 which looks like the following:

this means that currently we both:

1. don't allow download job to get added to the queue by checking the auth status in the controller (this may change based on What can make an API call [Discussion] #400 / what we decide to do with a ApiInaccessibleError signal in Timeout / No Auth #379 but at least for now in master it means the behavior isn't confusing) and
2. even if a download job is added to the queue, after log out it will no longer run and will raise ApiInaccessibleError

[sssoleileraaa]

lgtm with one nit

dismissing until i implement that nit / add more tests

[sssoleileraaa]

taking another look

[sssoleileraaa]

lgtm, my comments were addressed. just needs to be that follow-up issue and kushal was planning on reviewing this as well.

[redshiftzero]

cool thanks, followup added in #419, @kushaldas feel free to take this for a spin tomorrow

[sssoleileraaa]

we all decided that this looks good to merge w/o a second review, merging...

rip deauth queue