Make menu source selectable.

This patch provides several enhancements to this module.

1. It makes the menu source selectable from a dropdown list. This makes it much easier to chose a source for the menu. This uses a function from the menu.module so I also added a comment to the readme.

2. It makes the menu type selectable from a dropdown list.

3. It allows the user to rename the "Nice Menu" block to anything they want.

4. It makes the number of blocks selectable from a dropdown list.