Output spaces instead of tabs in buildAbout task

No Issue
Merge pull request #4318 from jaswilli/about-tabs

Output spaces instead of tabs in buildAbout task
Change slug and date placeholders to values

Closes #4121
Fix no show of default Twitter card

No issue
- change default Twitter card from content to summary
Merge pull request #4326 from lcamacho/master

Fixed default twitter card
Custom permalink UI

References #3920
Merge pull request #4323 from jaswilli/issue-4121

Change slug and date placeholders to values
Merge pull request #4217 from PaulAdamDavis/permalinks-ui

[WIP] Custom Permalink UI
Merge branch 'master' of https://github.com/TryGhost/Ghost