Refactor popup dialogs

[mborik]

Refactor popup dialogs to use uniform event handler from main thread, and get rid of while-loops within other parts of code.

• gui/CommonDialog.cpp > AboutDialog
• gui/CommonDialog.cpp > QueryDialog
• gui/CommonDialog.cpp > MessageBox
• gui/EditDialog.cpp > EditBox

Suggested steps:

• Extend GUI_MENU_TYPE with these dialog types (_ABOUT, _QUERY, _MESSAGE_BOX, _EDITBOX)
• Introduce typedef struct GUI_EDITBOX_DATA into UserInterface.h with all input parameters (title, description, buffer, maxLength, decimal), current state variables (x, y, w, len, cursor, result, atTheEnd, change) and sigslot::signal2<char *, BYTE> callback (sending buffer and result)
• Separate all key-handler switches from inner event loops to appropriate methods (KeyhandlerEditBox, KeyhandlerCommonDialog for About and MessageBox, and KeyhandlerQueryDialog) and integrate into MenuHandleKey
• Separate all GUI drawing code to appropriate methods (DrawEditBox, DrawAboutDialog, DrawMessageBox, and DrawQueryDialog) and integrate into MenuOpen switch

This is a prerequisite for the proper execution of the Emscripten/WASM build, where an additional infinite loop for polling events leads to the entire application becoming hung.