Static integration of the new PSM

Reference #3932

Take this, and make it work.
Enlarge mobile matchMedia max-width

Closes #3941

It now matches the mobile MQ in CSS - https://github.com/TryGhost/Ghost/blob/master/core/client/assets/sass/components/navigation.scss#L163
Bumping version to 0.5.2-1

no ref
- because Hannah said "someone"
Merge pull request #3935 from PaulAdamDavis/new-psm

[WIP] New post settings menu
Merge pull request #3943 from halfdan/patch-2

Bumping version to 0.5.2-1