Add reply w/ `Reviewed-by` tag of subset of patches from a series

[davidbtadokoro]

PR Commits

• First: Implement "raw" functionality to reply to a subset of patches from a series. It is "raw" in the sense that it doesn't implement a way to toggle the reply to all patches (which was the previous behavior) and doesn't update the UI component for this functionality
• Second: Implement the key bind uppercase R to toggle the reply to all patches
• Third: Update the UI to reflect the changes introduced by the third and fourth commits
• Fourth: Make UI display the list of patches that were replied with/ the tag as well, giving precedence to those over the staged ones and displaying them in a different color.

Closes: #78

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Example

Selecting patches 1, 5, and 7 from a series with 29 patches, in which patches 0, 3, 7, and 11 have already been replied with Reviewed-by.

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Steps to test this change

1. Sync your local repo with the latest unstable
2. Checkout to the latest commit of the unstable (commit 0bbf9c6e688a98c7b442b93990b63241c5dcd869)
3. Fetch and switch to this branch

   git fetch https://github.com/davidbtadokoro/patch-hub.git feat-reviewed-by-subset
   git checkout FETCH_HEAD

4. Launch patch-hub w/ cargo run --release
5. IMPORTANT: --dry-run is enabled by default, but, for sanity, check if it is indeed enabled by going to the configurations screen (F2) and checking the config git send email option.
6. Consult an arbitrary patchset, preferably a multi-patch series.
7. To stage a patch to reply w/ the tag, hit lowercase r. You should see the title Preview of the patch preview tab become Preview [REVIEWED-BY]*. You should also see the full subset of patches that have been replied w/ the tag and the ones staged in the Details tab as the entry Reviewed-by: (<patch-number-reviewed>,<patch-number-staged>*,...).
8. To (un)stage all patches, hit uppercase R.
9. To consolidate the reply of the staged patches, hit ENTER. This should tear the sleek TUI, and display the raw output of the underlying git send-email command.
10. After returning from the last step, there should be no patch staged to be replied to, no buttons [x] reviewed-by, and the patches that were replied to should be previewed w/ the title Preview [REVIEWED-BY] (without the asterisk) and show in the entry Reviewed-by: of the tab Details.

Any problem report or idea is welcomed, and thank you for testing this feature.

[davidbtadokoro]

@rodrigosiqueira, don't know if you've already tested this, but I've pushed a new WIP commit yesterday that changed a bit the display of the patches that have already been reviewed-by and the ones that are staged to be. I've updated the PR description w/ these notions.