Escape regex special characters in tag finder

refs #2149
- Properly highlight tags with special characters ($,[,],^,etc.)
Deduplicate upper-/lowercase tags for posts

server side check for #2478
- added check for duplicate tags in post model
Merge pull request #2496 from halfdan/more-tag-fuddling

Escape regex special characters in tag finder
Ensure generateSlug gets transaction for tags

fixes #2460

- add transacting to tag saving
- add same to users while we're here
Merge pull request #2502 from ErisDS/issue-2460

Ensure generateSlug gets transaction for tags
Merge pull request #2498 from sebgie/duplicate-tags

Deduplicate upper-/lowercase tags for posts
Bump version to 0.4.2-rc2
Error handling for require-tree

fixes #2507

- ideally we would create an apps directory if one isn't present, but we can deal with that in later versions
Merge pull request #2508 from ErisDS/issue-2507

Error handling for require-tree
Cache invalidation for tag pages
Updating Ghost-UI to 0.1.3
Version bump for 0.4.2
Fixing showdown link to work without git