Boards - Time in each column

[#1]

Description
I would like the option to display on the card how long it has been in a particular column.  

Why is this feature important to you

It would allow more visual management.  We could quickly see what has been where the longest and identify items that are stuck.  

How would you like the feature to work

I would like to be able to toggle on/off a "Days in current column" field.  I would like this number to display on the card in the Board view (i.e. without clicking on the card for details).  When the card is moved to a new column, the clock should reset.  

Current Behaviour

Currently this feature doesn't exist.  We have to leave comments each time we move a card to a different column.  This takes extra effort.  It also requires someone to open the card and scroll down to see this information.