Add ability to re-download content

Nobody has claimed this yet.

## The Issue
There are three main scenarios where users would want to re-download content in the LBRY app:

1) A claim was updated with a new source file - the user should be alerted to this and allow the new file to be downloaded. If the filename is the same, ask to replace or rename automatically If the content was paid for, it should not charge again (this may require https://github.com/lbryio/lbry/issues/803).

2) A download started (sd-blob downloaded) but then stalled. Currently, there's a workaround if the content is free but it takes a couple steps - you need to click "remove" which kicks you out of the claim page, so you need to navigate back. Then you can attempt to re-download. If the content was paid, this would not work since it would request a key fee again. Not sure if this is possible without https://github.com/lbryio/lbry/issues/803 right now.

3) Users already paid for content but the file is no longer available. If the blobs are available, can this be done without https://github.com/lbryio/lbry/issues/803?

Start by tracing the LBRY app's existing download, claim-update, and paid-content flows; no specific files or tests are named in the issue. Define acceptance criteria for replacing updated files, retrying stalled downloads, and restoring unavailable paid content without charging again, including the dependency on lbry issue 803.

Written by the indexing model from the issue text.