Improve CPU widget

[ClementTsang]

Description

A description of the change and what it does. If relevant, please provide screenshots of what results from the change:

This PR is part one of a change to the CPU widget.

This one focuses on:

• Removal of the old slash-space-to-hide behaviour of CPU widget

• Scrolling onto a specific entry will only show that entry

• Showing average is now default

Issue

If applicable, what issue does this address?

Closes: #

Does not close, but part of #156

Type of change

Remove the irrelevant ones:

• New feature (non-breaking change which adds functionality)
• Breaking change (if this change causes breakage or new behaviour, please state what)

Test methodology

If required, please state how this was tested:

Furthermore, please tick which platforms this change was tested on:

• Windows
• macOS
• Linux

Checklist

If relevant, see if the following have been met:

• Change has been tested to work
• Areas your change affects have been linted using rustfmt
• Code has been self-reviewed
• Code has been tested and no new breakage is introduced unless intended
• Passes CI tests
• Documentation has been added/updated if needed (README, help menu, etc.)
• No merge conflicts arise from the change

Other information

Provide any other relevant information: