[Coco theme] inconsistent margin/padding

[aoreucro]

The Coco theme text area has more padding on the top than the bottom, making the notifications look goofy. This is most noticeable with a simple notification like that produced with the following command:
notify-send 'Test';

I believe the issue is line 447 of /src/themes/coco/coco-theme.c:
gtk_widget_set_margin_start (vbox, 8);

The above is setting a top margin without a corresponding bottom margin (unlike the matching lines 428 and 429). I believe the solution is to add a call to gtk_widget_set_margin_end. Further, as I've also noticed that the top margin is a few pixels more than the side margins, it seems like the current margin should be split between the top and bottom. So line 447 would be replaced with:

gtk_widget_set_margin_start (vbox, 4);
gtk_widget_set_margin_end (vbox, 4);

Also, when an icon is included, the spacing to the left of the content (the content consisting of the combination of image and text) is less than the spacing to the right. I believe line 93 is the culprit:
#define IMAGE_PADDING 10

The above is from:
notify-send --icon=gucharmap 'Test' '________________________________________________________';

I think line 93 needs to be changed to:
#define IMAGE_PADDING 15

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