Add InsertText method

[ghost]

Added the InsertText method. The inserted text has the same formatting as the text at the cursors position. Additionally selected text gets replaced but the inserted one.

[ADefWebserver]

Please give me a week to look at this and test this out.

[ghost]

I've noticed while the method is working fine for something like a button, it's tricky for more complex components like a dropdown. If the editor has no focus you won't be able to insert anything. So I added a Focus method and test it out. It solve this problem but I'm unsure if it should be part of the InsertText method. I would rather keep them separate and let it be the developers responsibility to call Focus before InsertText if it's required.

[ADefWebserver]

Implementing things like Focus makes assumptions about the application that consumes the control. This is why I keep the control very simple.

I will merge the PR.

Thank You