Implement "Filter by codename" feature

[eloquence]

In the Journalist Interface, a journalist can type into the "filter by codename" field to quickly highlight a source they remember by name.

We don't have strong user research evidence one way or another whether this feature is actively used by journalists, and will include that question in the upcoming survey. Provided user research supports its inclusion, we'll want to provide similar functionality in the client.

Design

Final design work will be completed if user research evidence supports inclusion of the feature (see above). The current client designs include a placeholder for "search by codename" (example).

Acceptance Criteria

Given that I have more than 1 source in the SecureDrop client
When I start typing the name of a source into the "Filter by codename" field
Then it should incrementally reduce the list of sources to results that contain the substring I'm entering (not case-sensitive)
And the relative order of displayed sources should be unaffected

Given that I have more than 1 sources in the SecureDrop client
And I have previously filtered them
When I start erasing the contents of the "Filter by codename" field
Then it should incrementally broaden the list of sources, and ultimately show all sources again
And the relative order of displayed sources should be unaffected

User Story

As a journalist, I want to be able to quickly find a submission by typing part of the codename, so that I do not have to scroll through a long list of submissions.

[Please see the User Stories Spreadsheet for current prioritization of this story.]

[redshiftzero]

Just a note: while the current behavior on the JI is searching only by codename (since everything else is encrypted), since we added the content field to the database in the SVS VM, we can also enable searching the full text in submissions/replies, which seems more like what a user would naively expect.

(For a first iteration I think searching only by codename seems reasonable, I'm just flagging this so everyone is aware.)

[ninavizz]

Whence this issue gets tackled, making the note here to look at unifying the styling of single-line text entry fields between the main client pane and the login pane. The text entry box in this feature, and the text entry boxes on the login screen, are the only ones of this size (as I'm aware) throughout the experience, as of this writing.

[philmcmahon]

To add a user story to this - at the guardian we frequently need to find a source using their codename. We have a large inbox so it is often very difficult to find a source without such functionality. We use the built-in browser functionality extensively in the exiting journalist workstation