Fix reading tensor values from input.

- fix in fields/field_values.hh
- better coverage in field_const_test
Use std::string to pass EI_Address info.

... until we have Address class that persist after destruction of
the root input accessor.
Test output of all fields in 3D.

- minor simplifications in output*
- OutputTime::clear_data() is proper member and clear only
  data of particular object;
- move OutputDataBase declaration to separate file, necessary for tests
- implement correctly output of fields returning Fixed vectors
  and tensors of 2D space

- exception for variable size vectors