#791 Use ESCET logo/icon in ESCET IDE

• Best to review per commit.
• Changes:
  • Added ESCET icon as perspective icon, feature image, window images.
  • Added a new about dialog image.
  • Added a new splash screen image.
  • Added 96x96 pixels version of the ESCET icon.
  • Added ESCET icon .ico file.
  • Added ESCET icon to ESCET IDE Windows launcher.
• No icon yet for ESCET IDE Linux/macOS launcher. They require an XPM and ICNS icon, and I don't know how to make those.

Closes #791 (closed)