Version 0.20

+ Implemented new file using an empty XML template. (Cannot dynamically
create a new xml file from xsd)
+ Fixed Right-Click action 'Add' and removed 'Duplicate'.
+ Empty element items are not created in the xml file.
+ Added validation of xml values before saving.
+ Changed 'coordinates' child elements in XSD to be required if the
parent element exists.
+ Reworked 'About'.
+ Fixed Dirty File checking for save.
+ Fixed minor SaveAs dialog issues.
+ Added focus textbox on item name/rename.
+ Fixed a bug on rename-cancel.
+ Generated XML is now indented with tabs instead of 2 spaces.
+ Added restriction on multiple items, at least one must exist. (fixes
the parent 'Add' problem too)
+ Added logic on xml creation. If a group item is empty, don't create it
at all.
+ Added logic on item values validation. If a group item is not required
and
all it's children are empty, the group item valid.
+ Added Simulation>Create Graph action in the main menu. (Loaded xml
file name with .dat extension inside Samples)
+ Added last simulation time (last time modified .dat file) in Axis'
selection dialog.
+ Implemented move node (drag 'n drop) on tree viewer (with right-click
actions).
+ Automatically zooms out on diagram creation.
+ Added XML file validation before save.