InputText: checks whether provided content can be given
back unaltered, which may not be the case after it is
splitted to UTF8 chars if the text is binary content.
Prevent editing text if that is the case.
Adds InputText and InputDialog :isEditable() and :isEdited()
methods.
Also accounts for the scrollbar width when measuring text
to prevent it from being displayed when not needed.
Also ensure a minimal size of the scrollbar thumb so it is
rendered when huge text with many lines is displayed.
Virtual keyboard: Hold on Backspace: delete from cursor
to start of line instead of clearing all text content.
colors were a mixture of 4bpp integers (0=white, 15=black) and
fractional blackness levels (0=white, 1.0=black) before. This is
now unified to use the color specification of the Blitbuffer API.
