AIS_TextLabel - new public class to display simple text labels (based on MyTextClass private class from Draw Harness).
ViewerTest::Display() - add more reliable replacement for VDisplayAISObject() with no viewer update flag.
vdrawtext command redesign:
- Use new AIS_TextLabel class instead of private MyTextClass.
- Take object name and allow to clear labels from the Viewer.
- Use parameter name + parameter value syntax instead of strict list of mandatory arguments.
- Use [0; 1] range for colors and accept names.
- Drop redundant argument "isMultiByte".
- Support argument -noupdate to skip Viewer update.
Update test cases to new syntax of vdrawtext.
