Resize Edit Profile dialog only when possible

Summary:
Initial window width is set to be wider than (default) minimum possible
size. This adds some whitespace and increases width of text inputs
on "tabs" page.

This was made unconditionally, which could increase the width past
screen's right edge on small screens.

It is changed to be at most 2/3 of the screen's width now. Note that
minimum window size is still in effect; the limit affects only
additional width.

Test Plan:
(Instructions for X11)

* Run `Xephyr -dpi 96 -screen 800x600 :1`
* Run `DISPLAY=:1 kwin_x11`
* Run `DISPLAY=:1 ./konsole`
* Open edit profile dialog, resize it to minimum allowable size.
* Measure the window size.
* Close Xephyr.
* Run `Xephyr -dpi 96 -screen WxH :1`, where `W` is the measured window
  width + 20, and `H` is anything larger than measured height.
* Run `DISPLAY=:1 kwin_x11`
* Run `DISPLAY=:1 ./konsole`
* Open edit profile dialog

**Expected result:**
Edit Profile dialog's width should be a bit smaller than Xephyr's
screen

Reviewers: #konsole, hindenburg

Reviewed By: #konsole, hindenburg

Subscribers: hindenburg, konsole-devel

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D19400