DOM insert event support

[streamich]

• Support all beforeInput event types
  • Insert from clipboard
  • Insert from composition
  • Insert rich-text from clipboard
  • Insert Peritext rich-text
  • Insert image
  • Insert DataTransfer, file
  • Support all beforeInput inline formatting events
  • Support all beforeInput block-level events
• Support compositionstart, compositionend, etc. events.
• Support drag'&'drop events.
  • Image drop.
  • URL drop.
  • Rich-text drop.
  • File drop.