Monitor should retain 'mode' between showing/hiding

[kchadha]

Expected Behavior

Monitor mode should be remembered when monitor is hidden and shown again.

Actual Behavior

Monitor mode is not remembered if using the checkbox or the show/hide variable blocks.

Steps to Reproduce

1. Create a variable
2. Change the mode of the variable to a slider monitor
3. Hide the variable using either the checkbox or the hide monitor block
4. Show the variable using either the checkbox or the show monitor block
5. Notice that the monitor resets to the default variable monitor