HGBase Code (Desktop)

Correction of typos and docs.
Formatting.

Cache images for a given file name to read an image only once.

Extend functionality (used by tjger).

Add getAction method to menu.

Register actions instead of overriding onAction method.

Allows to register menu actions instead of overwritting onAction method.

Code format improvements.

Close stream.

Code format improvements and extracts an additional builder class from the menu.

Code format improvements.