UI issues

[w64bit]

1. "< 15" and "> 15" buttons width are too small.
   If you use a wider text, like Verdana, the buttons are displaying "< ..." and "15 ..."
   I think that it's better to increase the width for all buttons. Maybe 40 px?

2. The main window minimum width to be 400 px (to not allow resize smaller than 400).
   Not it is allowing too much horizontal resize leading to bottom buttons overlapping.

3. The main window minimum height to be 400 px (to not allow resize smaller than 400).
   Not it is allowing too much vertical resize leading to titlebar display only.

Instead, 2+3 can be achieved by not allowing resize smaller than the ini values ;Initial window size.

4. During horizontal resize (only when increase the width), the time and buttons are moved. They should not.

5. Do not allow multiple instances.