Create a command to clear all selections

[tngTUDOR]

Current

When a project/activity/method are selected, there is no way to clear current selection(s)

Expected

• add a command to clear all selections (from project to activity to method)
• add a command to clear the currently selected activity and keep project + database
• add a command to clear the currently selected database/activity/ but keep the selected project
• add a command to clear the currently selected method_namespace + method + category + subcategory