ContextMenus.cs: add MenuItem (in right+click menu in ChatTab) to open Hex_code-to-unicode Form.

ActionHandler.cs: add callout to open Hex_code-to-unicode Form (used by ContextMenus.cs).

SendBox.cs: add option to allow use of Up/Down key to move caret position (used by TextColoringPanel.cs)

SpringsettingForm.cs: use ZKicon for Form (Springdownloader icon)

TextColoringPanel.cs:
* window are resizeable vertically (bigger text editing area)
* add "Undo" button to undo mistake
* fix multiple issues with multi-line text editing and coloring

Add HexToUnicodeConverter.cs: a tiny Form that input Hex number and output Unicode character.

ZeroKLobby.csproj: add "Hex-to-Unicode" form to list of dependent file.

removed TextColoringPanel.resx: it contain no icon or image or anything in use.
TextWindow.cs: some random comment.