Update menu system and add back button use

Various changes throughout the code have been made so that the menu system integrates as expected on Android 3.0+ devices but still will use the menu button on older Android devices.

The manual was changed so that the Android back button is used.

I have not worked with code containing Japanese characters before, and I think that Eclipse garbled your comments that were in Japanese. For example, [this line](https://github.com/Vance-Turner/Maxima-on-Android/commit/e1751e642dd1fcf7b29b213e6aa9f473891f435e#L7L36) seems garbled. Could you check the Japanese comments? If they are garbled, I will remove the pull request, and try to fix my Eclipse setup.