fix #1232 Check tpl context still exists on widget

Just check that the associated template context for a widget still exists
before trying to execute a given callback on it.

Fixes #1232
Close #1233
fix #1226 Changing cursor for disabled list widget

Chaging the cursor from pointer to default for disabled items inside a list widget
feat #1234 Adding properties for Splitter widget

Adding new properties for borders for Splitter