Subscriptions: Wildcard for total subscribers in subscription widget

[yellyc]

The subscription widget has an option to display the current number of subscribers, but the text of the message cannot be customised.
To solve this, I have added a the option to add a wildcard in the widget text, "%d", that is replaced with the total number of subscribers.
The patch is simple and has been running on my live site for nearly a year now. I have opted to leave this as a "hidden" feature (it is not documented within the widget prefs), but text explaining this option can be easily added.
yelly

[yellyc]

A diff to add the "%d" wildcard to the subscription widget

[tmoorewp]

This patch doesn't allow customization of the text. We're going to be doing an update to the widgets in the near future soon and will take this into consideration.