force portrait mode, duplicate left input automatically; wipe inputs more often

Duplicating left input automatically might save people a 
couple of clicks when operating with scalars. If instead of 
clicking "=" the user clicks the right field, the field resets 
to zero so that the user can type normally.

Additionally, inputs are now wiped to 0.0 when clicking their respective fields,
rather than having to wait for a "clear" button. This makes the clear button redundant, and so is removed.
