Add support for printing time series and time series collection

[philipptempel]

Current version would filter time series and time series collections into cell of 'unknown' types. However, I feel, they are not unknown as time series are a quite nice and powerful feature and nothing domain specific.
Thus, this PR adds support to print 'Time series' and 'Time series collection', respectively, as type of the given variable.

Example of output of current version printstruct(stru):

stru
   |    
   |-- ts1 : [1x1 Unknown]
   |-- tsc : [31x2 Unknown]
   |-- ts2 : [1x1 Unknown]

Output with the version from this PR:

stru
   |    
   |-- ts1 : [1x1 Time series]
   |-- ts2 : [1x1 Time series]
   |-- tsc : [31x2 Time series collection]

Tested on: 8.6.0.267246 (R2015b) Mac and Win.