Minor changes of armor window

* Fix typo in "NEXT_TAB" action name (without this the scrolling of right window was broken).
* Change some minor things in armor_layer.cpp for further tweaking.
* Introduce the function <code>name_and_value (name, value, field_width)</code>

Example: <code>name_and_value("Safe Speed:", "234", 18)</code>
This code will put 4 spaces between "Safe Speed:" & "234" (because width of this text itself is 14).