[DMN Designer] Clear properties panel when multiple cells are selected

The user of the DMN Designer has possibility to set properties of expression grid table cell via properties panel. The problem occurs if multiple cells are selected. Then properties panel shows properties bound to last selected cell what is not desired. Properties panel should be empty if multiple cells are selected.

Manual acceptance test

Properties panel is empty if multiple cells (including headers) are selected

• Decision Table - fixed after reviews
  • 
  • Same for output columns
• Function
• Context
  • Multiple cells of same entry ==> properties for whole entry
  • Header and context entry - fixed after reviews
  • 
• Invocation
• Relation - fixed after reviews
  •