Standardize predefined Hand Configuration images

[stannam]

The predefined hand configuration images in src/main/resources/base/predefined show significant varitions. Notably, some images contain excessive empty space around the content, which makes them unrecognizable when rendered in smaller sizes within the hand configuration window (cf. #338). Also the images differ in size and formatting.

E.g., compare bent-extended-B.png vs bent-extended-U.png. The former has less empty space so it seems more recognizable when in a smaller size.

bent-extended-B.png	bent-extended-U.png

To make predefined images more useful/visible:

1. Trim empty space: remove excessive empty space around the content in all predefined hand configuration images.
2. Uniform background: Some images (e.g., clawed-5.png and pdhs_bent-R.png) have a white background while the majority has transparent background. standardize the background across all images to either all while or all transparent.
3. Uniform resolution: resolutions vary a lot. compare 1.png (367 x 377) vs. 8.png (2048 x 2048). I don't think we need a high resolution.