A complete rewrite of the IOTW code for creating the identity nodes hierarchy and exproting it to SVG.
Improvements:
  * The generation of identity nodes and their exporting to GIF/SVG is now completely decoupled.
  * The generation of identity nodes now excludes finding all the non-identity pairs that belong to it; whenever a single non-identity pair is found search stops there, since this is enough to asserts that the identity node belongs to the lower approximation (and not the higher approximation).
  * If someone wants to calculate the precision of an identity node, then this can be done by an additional predicate on a per identity node basis (since this can be very time consuming).
Todo:
  * The calculation of the precision of an identity node should be triggered by clicking on an identity node in the SVG output (using JavaScript).
  * The empty predicate node should be added (regression) to the exported hierarchy.