{{gh-path}} Handlebars helper, returning paths

- Uses utils/ghost-paths to resolve paths
- {{gh-path}} or {{gh-path ‘blog’}} for Ghost’s root (mysubdir/)
- {{gh-path ‘admin’}} for Ghost’s admin root (/mysubdir/ghost)
- {{gh-path ‘api’}} for Ghost’s admin root (/mysubdir/ghost/api/v0.1)
Remove unused, commented out CSS.

See #4102
Updating messages to use errors module

no issue

- only updated the messages that are errors or warnings
- changed the structure of the messages to follow the 3-arg format
Remove placeholders and limit SERP description

closes #4112, closes #4113
- Remove meta_* placeholders
- Add &hellip; in SERP preview when desc too long
Merge pull request #4115 from halfdan/4113-serp-placeholder

Remove placeholders and limit SERP description
Merge pull request #4127 from ErisDS/msg-update

Updating messages to use errors module
Fix leave modal when leaving new post

no ref
- set titleScratch to empty string if unset
Merge pull request #4129 from halfdan/fix-leave-modal

Fix leave modal when leaving new post
Incrementing hard limits for Meta title and Meta description

closes #4124
- incremented values for client-side validation for Meta title and Meta description
- changed error messages to display the maximum number of characters.
Fix post settings menu cog alignment and colours
SERP style updates
Fix padding on content preview mobile views
Minor start on CSS Style cleanup

See #4107
Mobile bug fixes for users view
Fix overly tiny text
Fix broken link, remove old html files
Remove about page header on desktop

See #4116
Merge pull request #4118 from JohnONolan/053-fixes
Disable horizontal scrolling in right outlet

Closes #4131

- Adds `overflow-x: hidden;` to `.right-outlet`
Rewrite publish bar markup

Closes #4123, closes #4114, references #4105

- Rewrite to use flexbox for über mobile goodness
- Fixes tag suggestions (using the new dropdown style)
- Fixes vertical alignment