Sublime Settings: Refactor value completions
Sublime Settings: Refactor value completions

- split methods to get smaller more readable pieces
- primarily use set() to create completions with unique items
- remove obsolete method arguments
- use common function to format completion items
- suggest list items instead of string representations of lists
- fix method comments
- add some checks to avoid exceptions by None objects' access

SublimeText/PackageDev,SublimeText/AAAPackageDev,SublimeText/AAAPackageDev