Convert some phutil_escape_html() to hsprintf()

Summary:
In the second phase, I want to get rid of the most of `phutil_escape_html()` calls in favor of plain strings or `PhutilSafeHTML`.
This is an example of how it could look.

Test Plan: /api/user.whoami

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4823
Convert setCaption() to safe HTML

Test Plan: /settings/panel/display/

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4824
Convert AphrontFormControl to safe HTML

Summary: Everything here now should properly handle plain strings and safe HTML.

Test Plan: /settings/panel/display/

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4826
Delete some phutil_safe_html()

Test Plan: Displayed revision.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4829