Add batch actions top bar element

[rocodes]

Status

Ready for review but presumes #2230 which should be reviewed first, will rebase once that's merged

Description

Add Top Bar UI element nested inside main layout, which will hold "Delete Sources" toolbar button (and eventually, other toolbar buttons). UI-only changes towards, #2160

Test Plan

• Visual review
• CI

Checklist

If these changes modify code paths involving cryptography, the opening of files in VMs or network (via the RPC service) traffic, Qubes testing in the staging environment is required. For fine tuning of the graphical user interface, testing in any environment in Qubes is required. Please check as applicable:

• I have tested these changes in the appropriate Qubes environment
• I do not have an appropriate Qubes OS workstation set up (the reviewer will need to test these changes)
• These changes should not need testing in Qubes

If these changes add or remove files other than client code, the AppArmor profile may need to be updated. Please check as applicable:

• I have updated the AppArmor profile
• No update to the AppArmor profile is required for these changes
• I don't know and would appreciate guidance

If these changes modify the database schema, you should include a database migration. Please check as applicable:

• I have written a migration and upgraded a test database based on main and confirmed that the migration is self-contained and applies cleanly
• I have written a migration but have not upgraded a test database based on main and would like the reviewer to do so
• I need help writing a database migration
• No database schema changes are needed

[cfm]

Rebased from main to kick the tires. Oddly, GitHub still shows a conflict with main, but we can resolve that in the course of finishing and testing this work.

[cfm]

Initial review. Since this adds a nonfunctional widget—the Delete Sources button is not wired up to anything—I'll review for real along with #2252 once that's ready.

[cfm]

You can eliminate the conditional with:

Suggested change

	def delete_multiple_sources(self) -> None:
	"""
	Requires logged-in session. Delete currently-selected sources.
	"""
	logger.debug("delete_multiple_sources triggered")
	if self.controller.api is None:
	self.controller.on_action_requiring_login()
	@login_required # from securedrop_client.logic import login_required
	def delete_multiple_sources(self) -> None:
	"""
	Delete currently-selected sources.
	"""
	logger.debug("delete_multiple_sources triggered")

[cfm]

I like the local style guide for "here's how to use this section of the UI". I'll note for the record that I continue to think that "batch" is an implementation detail of what is really just a "bulk" operation or an operation over multiple objects—not all of which will batch the individual operations or requests. I'm fine with whatever terminology we adopt as long as we don't wind up confused by it.

[cfm]

I'm inclined to merge c8aecc3 as part of #2252. I think the separation is too minimal by now to be worth the rebase from here. What do you think, @rocodes?

[rocodes]

yeah I agree - might as well close it and merge them together. I was initially trying to split up the work into readily reviewable chunks so that people could tag team as needed, but might as well just do all in #2252.

[rocodes]

Closing in favour of #2252