Track when crates are yanked and handle yanked status better

[Nemo157]

• mark releases as yanked when a yank is detected
• show yanked status on crate details page
• don't redirect to a yanked version if it's the latest
• add test to load handlebars templates
• Don't show latest version redirect to yanked versions
• Allow loading yanked docs via exact version number
• Show yanked status in nav on rustdoc pages
• Show yanked status on crate details version list
• Show yanked status in version drop down

I skipped 7a57350 from #322 to avoid any conflicts with #721, it may be useful to look into rebasing that too later.

fixes #112, #396
closes #322

Screenshots:

nav bar when viewing latest version and all versions are yanked:

nav bar when there's at least one non-yanked version, or viewing non-latest version of a fully yanked crate:

crate details page:

crate details version list:

crate details nav drop-down:

[jyn514]

cc @QuietMisdreavus :)

[jyn514]

Oh boy, we have some technical debt stacking up. Once this PR is in I think we should start think about getting things by name instead of by index: https://docs.rs/postgres/0.15.2/postgres/rows/struct.Row.html#method.get

[jyn514]

get_platform_links is pretty similar to this, do you think it's worth factoring out a html_select() function?

[jyn514]

Waiting for https://github.com/rust-lang/docs.rs/pull/739/files#r418711919, https://github.com/rust-lang/docs.rs/pull/739/files#r418711559 to be addressed.

[jyn514]

Same comment as #746 (comment)

[jyn514]

Suggested change

	assert_eq!(
	env.frontend().get("/crate/dummy").send()?.status(),
	StatusCode::NOT_FOUND
	);
	assert_eq!(
	env.frontend().get("/crate/dummy").send()?.status(),
	StatusCode::NOT_FOUND
	);
	assert_eq!(
	env.frontend().get("/dummy").send()?.status(),
	StatusCode::NOT_FOUND
	);

[jyn514]

Whoops, I misread the changes. You addressed both the comments I linked.

[jyn514]

Looks good once nits have been addressed.