Added deadline miss counter to FrequencyTable

- for each time (key) in FrequencyTable we now have: one counter for number of occurrences, and one counter for number of times task missed deadline when it had this time 
- works for both response time and jitter (and any future time we might store in FrequencyTable)
- the only way to see this new data is to use toString of Frequency table (that's even how it's unit tested)
- TODO figure out a way to use this new data in an elegant fashion