Added new button implementation
Merge branch 'button-implementation' into wdat2-develop
Container class
Documentation and bugfixes for container
Fixed some bugs in Tree (expand(), add())
Fixed bug in Tree.select()
Small bugs fixed in Tree
Button bug/feature fixed: button events now deliver their data object and not the button objec itself
Tree bug with actions fixed. Tree should be without any bug now
Tree test works fine
Version v0.13.0 Tree refactoring complete
Merge branch 'tree-implementation' into wdat2-develop