move user-line-extension logic into its own package
remove parameter never used
regroup ULE logic into common manager

user_line and line_extension have some code in common,
but it's all over the place and isn't well structured.
This is the first step towards refactoring it.
implement ULE helpers when associating a user, line, or extension
refactor user_line and line_extension to use ULE services
implement ULE dissociation in ULE services
remove unused function
use user_line.main_user instead of searching the DB

reason: make the condition clearer
Merge branch '5003_restapi_incall'