Jumpy centering of modal dialogs when browser window is being resized

[ashklianko]

@alansemenov commented on Mon Sep 18 2017

1. Open the browser window to be about 800p or wider
2. Open the Issue List dialog
3. Start resizing the window by decreasing the width

When the window is about 675px wide the dialog starts behaving weirdly, jumping to the left side and then centering again. It also changes height.

The dialog should not change height and it should always remain centered (or take the entire width, on lower resolutions), like the "New content" dialog for example.