Split view for editor

[vparfonov]

"Side-by-side editors to simplify working on larger applications."
split vertically/horizontally, for instance when right clicking the editor tab it should be possible to split editor vertically or horizontally.

• Sync content of the file for all opened tabs of this file Sync content of the file for all opened tabs of this file #1838
• Correct processing some operations for editor Correct processing some operations for editor #1839
• Adapt Editor agent to manage multi parts Adapt Editor agent to manage multi parts #1840
• Improved tabbed editor design Improved tabbed editor design #1841