Use curl for downloading, standardize paths in UpdatePane[CPP-502][CPP-505]

[john-michaelburke]

• Use reqwest for downloading firmwareCPP-502
• Fix backslashes for stings in UpdateTabCPP-505

[silverjam]

If the UpdateDownloader is allocated "statically" (as in, it sticks around for the whole app) it could account for the memory increase. We can switch to a dynamic allocation if that's the case (and drop or zero the downloader after using it) and it should resolve the memory issue.

[silverjam]

This PR walks back some dep updates, not sure if that was intentional, fix proposed here: #303

[silverjam]

Something else must be statically/globally allocating memory in the chain of new libraries pulled in by reqwest. Reqwest depends on Tokio, which is a new, large dependency for us. Maybe we cant try https://crates.io/crates/curl? We'd probably need the the "ssl" and "static-curl" features.

[silverjam]

Attempt to use curl here: #304

[silverjam]

Attempt to use curl here: #304

Same failure, so my theory doesn't seem to be correct, perhaps the increase was unrelated to the changes here, but still curious... but I don't think we should block this change over 9mb of memory though (and as long as this isn't indicative of a leak) I think we should just bump up the memory limit.

Also, if curl is still faster than minreq I think we should keep it, it's a much smaller dependency than reqwest (if we were already using tokio then it would not be an issue, but we've avoided tokio up to this point).