Support for undo and redo functions in interface
Merge branch 'master' into interface
Updated classpath to include natty lib

natty-0.9.jar will be used as an approved date time lib to parse dates
from natural languages.
Added diagrams folder and diagrams (interface)

For more coherent and unified place to store diagrams for easy
references.
Merge branch 'master' into interface
Merge branch 'interface'