The merge layer button looks too much like a download graphic.

[JasonHoku]

I and another user both didn't recognize it as merge.

It could be updated to be more intuitive and less confusing by using a more clear merge icon instead.

I tried for a bit to understand the code base deeply enough to submit a PR for this issue but I don't think I understand the frameworks well enough.

I found the classname for the icon here in \piskel\src\css\font-icon.css at line 62

.piskel-icon-merge:before {
  content: "\e609";
}

And found mention of the unicode symbol as a glyph in this file: \piskel\src\css\fonts\icomoon.svg

But that seems to be where my mission comes to an end.

Would you all accept a simple svg and html replacement PR?