enh(ui) better menu delimitation

[EdytaSki]

Pull Request Template

Description

Please include a short resume of the changes and what is the purpose of PR. Any relevant information should be added to help:
You should see a grey border on the right side of the left menu.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• New functionality (non-breaking change)
• Breaking change (patch or feature) that might cause side effects breaking part of the Software
• Updating documentation (missing information, typo...)

Target serie

Please delete series that are not relevant.

• 18.10.x

How this pull request can be tested ?

You should see a grey border on the right side of the left menu.

Any relevant details of the configuration to perform the test should be added.

Checklist

Community contributors & Centreon team

• I followed the coding style guidelines provided by Centreon
•  I have rebased my development branch on the base branch (master, maintenance).

* updating the release note results in adding the pull request id and description at the end of the file. Product Managers will rework it for the release. Release notes can be found here.

Centreon team only

• I have made sure that acceptance tests related to the story are successful (local and CI)