messages: Implement logic to display poll widgets.

lint-and-test: Run Python 3.7 tests under ubuntu 22.04 for now.

messages/views: Prepare for the deprecation of user metadata.

model: Add handling for Submessage events.

core: Reword end of exception popup to motivate reporting.

refactor: core/model: Rename popup_with_message.

keys: Add new help category for user list actions.

mailmap: Add entries for Niloth P & Sashank Ravipati.

FAQ: Add entry discussing composing messages in an external editor.

gruvbox_light: Support transparency in gruvbox light theme.

core: Center the save_draft_confirmation_popup.

keys: Improve descriptions of hotkeys that switch narrows.

keys: Rename the help category of message compose box actions.

refactor/bugfix: helper: Normalize file path in process_media.

keys/ui: Add hotkey and command to generate new random footer hint.

keys/boxes: Convert remaining GO_BACK command use into EXIT_COMPOSE.

api_types/model: Fetch stream email address from endpoint if required.

keys: Add space key as an additional trigger of ACTIVATE_BUTTON command.

tests: popups: Add test for content copied from About popup.

keys: Standardize choice of words in hotkey help texts.

keys: Improve descriptions of editor hotkeys.

gitlint: Add regex to ignore some long lines.

bugfix: github: Adjust label yaml quoting syntax.

github: Add preliminary issue templates & configuration.

boxes/views: Adopt urwid_readline for all editors.

api_types/model/boxes: Add read_by_sender when sending messages.

Update issue templates

api_types/model/boxes: Add read_by_sender when sending messages.

lint-hotkeys: Add missing '--fix' flag in usage prompt.

refactor: core: Use a common scroll prompt in popup headers.