Override AddPanelAt in TabbedEditor

[nelsam]

Dragging panels between tabbed editors was causing the new tabbed editor to add the panel as a child without also storing that editor in its map of available editors. This meant that the next time something tried to focus the editor, it would open a second copy of that tab.

This fixes that issue.

Resolves #107

Type

• [x] Bug Fix
• [ ] New Feature
• [ ] Quality of Life Improvement

Tests

I have tested locally against:

• [ ] Windows
• [x] linux
• [ ] OS X
• [ ] BSD

I have included automated tests:

• [ ] Unit tests
• [ ] Integration tests
• [ ] End to end tests

[nelsam]

@Kvaz1r this should solve #107 - could you build from this branch (107-duplicate-tabs) and see if it solves the issue for you?

[Kvaz1r]

yes, it's works for me.

[nelsam]

Cool. I'll merge after travis gets around to running the build.