Magic UV: Release v5.2

* Bulit-in menu preferences
* Add-on updater

* Copy/Paste UV
  * Add option "[New]" for pasting to newly allocated UV map
  * Add option "[All]" for pasting all UV maps at once
* Align UV
  * Add option "Mesh Influence"
* World Scale UV
  * Add mode option "Manual" to allow the user specify the density manually

* Improve UI
* Cleanup documents
* Fix bugs