custom slugging capabilities for individual user pages

closes #3401
- modifying slug-generator to be more generic
- adding slugging capabilities for /settings/users/:slug
- modified posts to use the updated slug-generator
Keyboard shortcuts for Mac vs All

Closes #3029, Ref #3469
- Editor shortcuts are now built in a separate file, which uses `ctrlOrCmd` to correctly set OS specific shortcuts.
- Removed `newLine` and `selectWord` shortcuts
Merge pull request #3471 from novaugust/editor-shortcuts

Keyboard shortcuts for Mac vs All
Merge pull request #3472 from morficus/issue-3401

custom slugging capabilities for individual user pages