Rename click/open/close "commands" to "actions"

[BlitzOffline]

DeluxeMenus supports more than just commands execution and so I believe "actions" would be a better suited term.

I think a fair transition would be as follows:

• we add new options: click_actions, open_actions and close_actions
• after the change was uploaded to spigot we update the wiki to only show "actions" instead of "commands
• we support "commands" for a few updates
• we remove "commands" support in favor of "actions"
• one optional step would be a simple app that replaces all instances of strings such as "close_commands" to "close_actions"

The only issue to be discussed is how having both "commands" and actions for an item would work.
My initial idea would be to completely ignore "commands" if "actions" are specified as this suggests the user is aware of what "actions" are and why they were added. Also, giving a warning in console together with the previously stated solution sounds fair to me.