Platform agnostic common dialogs support

[a740g]

We should provide a way to support common dialogs (like MessageBox, InputBox, PasswordBox, ColorPicker, OpenFileDialog, SaveFileDialog, SelectFolderDialog, Tray-popup, Notification Beep) in a platform agnostic manner.

libqb.cpp already has rudimentary support for MessageBox & Alert. However, these can be significantly improved and extended.

From my observations most folks resort to calling native OS libraries for these functionalities which ties the code to a particular platform. Also, supporting common dialogs for multiple platforms on the BASIC side is rather complicated and complex.

My recommendation is to use a tried, tested and compact library like tiny file dialogs.
Using this we can then have VB-style dialog functions like _GetOpenFilename, _MsgBox, _InputBox, etc...

[ghost]

I like this idea. I don't typically do cross-platform code so when I do dialogs they always are platform specific. However, I could cut down on BAS code by having an internal dialog function like this.