Input variables

Currently, the values of the xbook input variables are hard-coded (very bad!). We need to provide a mechanism by which input form values can be read in from a file, the simplest format being a java PropertiesFile format (i.e., name, value pairs):

  <name of input form variable>: <value of input form variable>
  <name of input form variable>: <value of input form variable>
  ...
  <name of input form variable>: <value of input form variable>