File tab implement for GUI enhancement.
- I have customized the elm_list's theme to look more like a regular tab.
[file click on explorer -> file preview]
the preview tab is activated whenever you select another file in the explorer.
only one preview tab is created, and the text style of tab is Italic.
[file double click on explorer -> pin the tab]
pin the selected tab to the top. you can close by pressing x button.