Improve file list widget

[imagejan]

• Set button label to Add files... or Add folder... depending on widget style
• Added Add folder content... button with drag-drop support to allow adding files matching the extensions defined by style from a folder and sub-folders

To test the full functionality, use the following script:

#@ File[] (style="extensions:tif") fileList
#@ File[] (style="directories") folderList

println fileList
println folderList

• use buttons and/or drag-n-drop (onto the list field, or onto the Add folder content... button) to populate the list
• double-click on list entries to remove them

[ctrueden]

Very sorry this sat for so long, @imagejan. It looks really nice. I was just wondering one thing, about the direct usage of JFileChooser rather than leaning on the UIService file choosing methods. What do you think?

[ctrueden]

Instead of doing this: can we use uiService.chooseFiles? Then we can have this threading logic solved properly in a single place.

[imagejan]

Good suggestion, I'll change this.

[imagejan]

I ended up using ui() instead of uiService because I'd otherwise get the Legacy UI's directory chooser, which led to some of the Swing buttons not being rendered correctly (not "released" after drop), and the look-and-feel being changed when running the example script a second time.

When using ui(), we keep using the SwingUI for both the dialog and the file chooser, which worked fine in my tests. (I also replaced uiService by ui() in the other place where it was used, and thereby got rid of the UIService parameter.)

@ctrueden if you have no concerns with this, I'd say this is ready to be merged.