Removing the concept of time interval

[dreamer2368]

BasisGenerator, BasisWriter, BasisReader, and SVD classes use the concept of time interval, assuming snapshot/basis for multiple time intervals. However, this has never been used in practice, and rather complicates the code implementation. It is decided to remove this concept, enforcing single time interval from PR #261 .

• Options class and the classes above should not be initialized with max_time_intervals.
• Snapshot and basis datasets should not be named with the number of interval.
• loadSamples, takeSamples, computeSVD, and etc should not use the number of interval, assuming single time interval.

[dreamer2368]

This is addressed by #261 .