Update folder file count badge presentation

Match the presentation of the number of files in a folder to what WP File Downloads does with the number in paranthesis vs. a solid circle with a number in it. This will make the two products more closely aligned and also calls less attention to the number of files vs. the name of the folder and which folder's currently selected. By having all the file counts highlight blue, it adds confusion to which folder is currently selected. Also having the folder background/row highlighted slight further identifies which folder is currently active and allows the eye to easily see which file count is related to the folder currently selected. The highlighting of folders when hovering over them is also helpful. In fact, copying a lot of what WP File Downloads does for its tree view over to WP Media Folders would be nice