Add a command to sort tabs by name

[Tragen]

E.g you have a tree
TAB

• F
• D
• A

and you sort it, you get

TAB

• A
• D
• F

[piroor]

Note: I have less motivation to implement new features by my hand, and pull requests to implement "good first issue" labeled features like this are always welcome. I hope these issues get people involved to join opensource development.

A new keyboard shortcut will be added here:

tst-more-tree-commands/manifest.json

Lines 48 to 49 in c18b790

	}
	},

tst-more-tree-commands/background/background.js

Lines 354 to 355 in c18b790

	return;
	}

Codes for a new menu command will be added here:

tst-more-tree-commands/background/background.js

Lines 155 to 156 in c18b790

	}
	};

tst-more-tree-commands/background/background.js

Lines 225 to 226 in c18b790

	default:

tst-more-tree-commands/background/background.js

Lines 284 to 285 in c18b790

	default: