Make menus more consistent and intuitive

[libalis]

Before all: very first pull request ever, so sorry for everything.

This pull request changes the following things:

1. I noticed an ugliness in the formatting.

2. The about dialog has moved to the bottom.
   This is more consistent and intuitive in my opinion, as it is a rather unimportant item.
   An application menu should probably have the applications at the top.

3. Made separators consistent.

Opinions are welcome.

[ghost]

This is a helpful change from a UX perspective. Now the XDG menu is at the top.

[stefonarch]

It was me who created "compact" and "single" menu. My idea was to move "About" out of the way (on top for a bottom panel) as this entry is used very rarely normally. Thinking about it offering an inverted menu for top panels could be a good idea, with "search..." on top.

And I think there is no need for the menu to be "consistent" among them - again, the idea was to offer alternative layouts.

[tsujan]

Thinking about it offering an inverted menu for top panels could be a good idea, with "search..." on top.

"Search" is an item in the menu. With an inverted menu, every item should be inverted. IMO, such a menu will look unnatural.

I don't see any benefit to putting "Search" above the menu and keeping the other items as they are either (I use a top panel) but I'm not against its implementation (which I think isn't trivial).

As for this PR, I think it's a just matter of taste and there are as many tastes as users.

[stefonarch]

I didn't think of inverting all, just about "search" and maybe "leave" on top.

PS: for some reason I saw this PR only today.