Added numeric-only editing mode for edit box widget

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Added password edit mode to edit box widget

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Cleaned edit box widget code

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Implemented text selection in edit box widget

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Added missing commentary to utf8_strncpy

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>