Adjusting menu colors, active and hover effects on LCARS theme

[rdwebdesign]

What does this PR aim to accomplish?:

• Better colors for menu groups, hover effect and active menu item.
• clean old and unused styles.

How does this PR accomplish the above?:

• New CSS using variables to simplify the code.

What documentation changes (if any) are needed to support this PR?:

none

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[yubiuser]

The animation during sidebar closing looks really smooth. But when the sidebar expands, it suddenly removes the left part of the light blue bar and starts only afterwards to collapse. Maybe you can prevent the sudden blackness?

[yubiuser]

Add: also during collapsing, the light blue bar extends a bit and closes the small black gap....

[rdwebdesign]

Fixed.

[yubiuser]

It's still a bit floppy on mobile. I tried to capture it on using dev tools/mobile, here it does not happen every time, but on real mobile it's always happening.

[rdwebdesign]

I think the problem there is the animation speed combined with the "custom" background.

The sidebar and the content-wrapper elements are moving in slightly different speeds and you can see a "gap".

To adjust the animation we will need change the javascript in adminlte.min.js.

I don't want to do it.
This is a small glitch, in just one theme.