Viewport jumps when handling long text

[Allerby]

Firstly, thanks for this great addon wrapper!

I've just noticed what I think may be a bug when the simple-mde textarea gets provided a large string of text. When you scroll down the editor a little bit, then start editing - the viewport jumps to put the cursor at the bottom of the page. Behavior can be seen In the twiddle below:

https://ember-twiddle.com/cdde8fcc6b9a1b1136f681316d1b380f?openFiles=controllers.application.js%2C

[marceloandrader]

Hey @Allerby I was able to reproduce it locally too, I think the issue is in this lines:

https://github.com/smith-carson/ember-simplemde/blob/master/addon/components/simple-mde.js#L123-L125

We need to update the value on the editor from the value passed by the attribute value, to keep the cursor where it need to be I got the initial cursor, update the value, then set the cursor where it was (If not it will always take you to the beginning of the text)

I see that there is another function called setSelection that receive some options to avoid scroll, but I wasn't able to make it work. As always in open source pull requests are welcome.