Fix up HTTP API handler

No Issue
- Add Location header for tags.
- Ensure Location header has trailing slash.
- Remove unnecessary promises/async.
Fix invalid HTML in templates.

HTMLBars (coming soon in Ember 1.10) validatest templates during
compilation. This PR fixes errors identified.
Merge pull request #4727 from rwjblue/fix-template-html

Fix invalid HTML in templates.
Remove PostSettingsMenuView.

It seems that the properties this sets up (`datePlaceholder` and
`publishedAt`) are unused throughout the project.
Merge pull request #4728 from rwjblue/remove-unused-view

Remove PostSettingsMenuView.
readme.md edit

-missing comma
-use of "a" preceding an acronym with phonetic vowel
Merge pull request #4730 from sdtsui/patch-1

readme.md edit
Update README.md
Revert punctuation change in README.md
Removed double link, moved contributing ref.

- Contributing ref link was being gratuitously double-linked to, nixed that.
- Changed grammar which is ambiguous between US/UK colloquialism.
- Moved contributing/troubleshooting reference to "installing from git" heading rather than "quickstart" subheading
- Standardised 2-linebreaks between Markdown headings
Merge pull request #4724 from jaswilli/http-api

Fix up HTTP API handler
Change url and image into synchronous helpers

Closes #3961