Implements is-helper

closes #2249
- Added context to res.locals
- Added context aware is helper
- Added unit tests
Fix chevron animation in publish button

Closes #4104

- Fixed the broken spiny animation used in the publish button
Merge pull request #3962 from halfdan/2249-is-context

Implements is-helper
Merge pull request #4117 from PaulAdamDavis/fix-post-state-arrow

Fix chevron animation in publish button
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.