Datatype functionality enhancement

[alasheen]

• [x] Option to return a time based datatype using the reshape function with use_time

The present implementation should return a timebase='interpolated' datatype but returns timebase=None instead.

An option to return a timebase==by_time datatype would allow to reuse the time information when combining several datatypes (e.g. for combine_single_sections function).

• [x] Addition of datatypes with other types

E.g. to add a single float value to a time based datatype, or two time based datatypes

• [x] Adding interpolation to the data_type dict

E.g. for combination of functions, copy() function...

• [x] Extend single valued datatype when time base is passed

• [x] Check try/except loops in combine_single_sections

[scpalbright]

All done, included on upcoming pull request #48