ha-sidebar: exclude some items from scrollable + fade + various fixes

[ildar170975]

Breaking change

Proposed change

What this PR does:

1. Fix a height for the bottommost ha-md-list containing "notifications" & "user profile": currently the height is set to some calc(100% - ...) - but this should only be done for the 1st ha-md-list containing other panels. This causes a wrong vertical spacing between a user avatar & a bottom boundary.

2. Exclude 2 last item - "dev tools" & "config" (along with possible "ExternalConfiguration") - from a scrollable list (see screenshots below).

3. Fix a tooltip for a user profile - there was an error in a "span" element (also fix a similar imperfection for a "config" badge span, did not cause an error since a value inside a span was a number instead of a text) (also a similar error for an "external_app_configuration" span).

4. Reduce top/bottom paddings for a "divider" element (located above a "notifications" item) for a bit compact look (the 1st fix can be seen here too):

5. Add ScrollableFadeMixin to a scrollable area:

6. Remove _externalConfig from shouldUpdate() - it is not present in a code (may be left from a past?).

WORKS IN PROGRESS !!! Some issues are still to be solved.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example configuration

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io