Fix duplicate download IDs when using "/url save"

[ike08]

Fixes #1794

Explanation
The problem is the download's identifier. Downloads are given an ID so they can be referenced later when their progress changes. Currently, the download's ID is the download's URL. When you download the same file twice, you have two downloads with the same ID. Download progress updates are shown on the first of both downloads with the same ID.

Solution
Change the download's ID from its URL to a random number. There is a new function in cmd_funcs.c named "_url_make_id()" that generates a random number for a download's ID. Several other functions are updated to cope with the new ID format.

[jubalh]

A couple of git things:
You have merge commits in there. They shouldn't be there. You want to rebase on master not merge it into this branch.
Also on some commits you are Your Name. And on others you set your email properly and GH recognizes your login.

So I would suggest to remove the merge commits, squash your two commits into one and set your name/email as you want it to be displayed.

If you don't want to do that I can also cherry pick/squash myself.

Also you changed the coding style somewhere. Which makes our CI complain.
As mentioned in https://github.com/profanity-im/profanity/blob/master/CONTRIBUTING.md clang-format can help with that.

[jubalh]

See comments

[jubalh]

Looks good now. Would you mind to expand the commit message?
Like use what you already have as the title. then have a new line. then paste what you wrote here on github already, your first comment. Which mentions the issue it fixes and explains how/why.
That would be great.

[ike08]

I think I made all the changes you requested. Let me know if you find anything else that is not right. Thanks