Add a method to get the status of SuspendTimerCallbacks()

[tstanley]

It would be convienent at times to have a way to know if timer callbacks had been suspended by another part of the program by 

SuspendTimerCallbacks(), or if timers are running again from ResumeTimerCallbacks().  As far as I can tell there is currently no way to know this in CVI without manually keeping track of the last suspend/resume function called.  Thanks.