Handle 404 properly

[Calvinp]

Handles 404s on pages for specific requests, deploys, and tasks by showing the 404 page rather than rendering something meaningless and showing an error.

The following pages are affected:

• DeployDetail
• RequestDetail
• TaskDetail
• New Deploy Form
• Edit Request Form

Please let me know if I've missed any @tpetr @kwm4385 @wolfd

[Calvinp]

Looks like it's not going to be possible to detect 404 on Task Search right now.
The server responds with an empty array rather than a 404, even when using the /request/:requestId/task-search URL.
@ssalinas a possible future improvement to the Task Search API would be to 404 when the request isn't found in this case.

@tpetr @kwm4385 @wolfd This PR is good to be reviewed/merged from my perspective now.

[wolfd]

What does this mean?

[Calvinp]

Unfortunately the meaning snuck into another PR - that's on me, I implemented it with the Deploy Detail page fixes.
It's basically an idiomatic way of saying it ignores 404s. It signifies that if the API call fails with a 404 then the page should 404 (but it can also be extended to mean other things later).

[tpetr]

isMainApiCall doesn't convey that information at all -- if that's all that this variable controls, can we think of a more descriptive name for it?

[Calvinp]

Naming things isn't my strong suit. Maybe pageCantRenderIfThisFails? I don't really like that name either though.

[Calvinp]

Or page404sIfThis404s.

[tpetr]

It's cool, naming is hard 😄 -- I'd suggest something like renderNotFoundIf404

[wolfd]

LGTM

[tpetr]

LGTM