Add icon to search bar

[amias-scribe]

Hello! I will hopefully be implementing Notepad++ as one of the tools used across multiple teams at my organization, and NPPSnippets is very useful for the process I will be teaching others to use. In the interest of general UI legibility, I suggest adding a magnifying glass icon to the search bar in the Snippets panel.

Thanks for making a plugin that does exactly what I was looking for in NPP!