Return safe HTML from all render()

Summary:
This is pretty brutal and it adds some `phutil_safe_html()`.
But it is a big step in the right direction.

Test Plan: None.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4905
Merge renderSingleView() and renderHTMLView()

Summary: They are same because render() returns safe HTML and raw strings are automatically escaped.

Test Plan: None.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4909
Merge renderChildren() and renderHTMLChildren()

Summary: `renderChildren()` now returns array which isn't ideal but I prefer it to having two methods.

Test Plan: None.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4910
Fix some HTML problems

Summary: I'm too lazy to attaching them for diffs where they were introduced.

Test Plan:
/
/D1, wrote comment with code snippet
DarkConsole
commit detail, wrote comment
task detail, wrote comment

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4911