Add 'other mortality' input

[villyc]

On the basic input form. Add a new input: "Other mortality". If EE is entered, then "Other mortality" should be blocked, and vice versa. If it is entered, e.g., as 0.1, it is the same as entering an EE of 0.9. With this we don't need to explain EE. When I run courses I tend to explain EE based on "other mortality" so we might as well make it explicit.

[jeroens]

Implemented 28Feb11