Implement palette based images and loading of images from storage

[davetcc]

This is to implement the loading and display of palette-based images, from either flash to start with, storage-based mediums will be implemented later.

[davetcc]

To start with we will just create/improve the storage interfaces so that load from file could be implemented later. For now we'll support only flash-based images in 1, 2, 4 and 8 bits per pixel.

We'll support this onto LTDC, TFT_eSPI and AdaFruit_GFX TFTs. The create bitmap UI in the designer will be improved to be able to save these out.

[davetcc]

Step 1 in place, it is now possible to express a palette based image within a drawable icon, next step will be to draw it using device drawable.