[SLD] Fix connectable order

[rolnico]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• A PR or issue has been opened in all impacted repositories (if any)

Does this PR already have an issue describing the problem?
No

What kind of change does this PR introduce?
Feature

What is the current behavior?
In SLD, the elements displayed are not sorted, which can result in having differences in display of the same network over time.
In SLD, streams are computed through vl.getConnectableStream(<Class>).

What is the new behavior (if this is a feature change)?
In SLD, the elements displayed are now sorted.
In SLD, streams are computed through the specific methods (for example vl.getLineStream())

Does this PR introduce a breaking change or deprecate an API?

• Yes
• No

If yes, please check if the following requirements are fulfilled

• The Breaking Change or Deprecated label has been added
• The migration steps are described in the following section

What changes might users need to make in their application due to this PR? (migration steps)

Other information: