Fix system.hh for case without HAVE_PETSC
Replace get_field by operator[].

- overload operator[] (returns reference, and throws for unknown name)
- field() method returns pointer (nullptr if not found)
Distinguish field "name" and "input_name".

- introduce Field<..>::name attribute which identifies
  the field in a FieldSet
- distinguish this from input_name used to declare and read appropriate key
  in the input filed descriptor
- introduce methon input_name() to read the input_name
- rename setters used just for input
- fix unit tests
Merge branch '1.8.0_master' into JB_finish_fieldset
Temporary fix for wrong ASSERT.
Introduce FlagArray.

- bitfield like class that allows setting and testing
  arbitrary subset of bits.
Introduce FieldFlag class.

- this class just defines FlagArray type used by Field classes
  and common Masks to set and test
- in order to make these masks easily accesible from FieldSet, we make
   FieldSet descendant of FieldFlag
- add FieldCommonBase::flags() getter
Replace FieldCommonBase::just_copy() method

- remove the method, remove is_copy member
- replace it by flag declare_input turned off
- introduce mask input_copy to this end
- add constructor of FlagArray from a Mask
Fix missing include.

- add missing conditional include of petsc.hh
Apply field_flags.

- minor change in flags interface, renaming 'set' method to 'add' method
- apply flags in Sorptions and Transport
- try to remove some virtual methods in Advection Models
Refactor fields.

- rename FieldBase<> template to FieldAlgorithmBase
- rename its files to field_algo_base.*
- rename*_impl.* to *.impl.*
FieldSet::set_n_components

- add FieldSet::set_n_components
- rename FieldCommonBase::n_comp to set_n_components
- apply in Sorption,DualPorosity, TransportDG, Transport
- comment out init_data method of Trnasport models
Stateless FieldSet

- try to remove additioanl attributes from FieldSet
- adapt Filed assignment operator to not copy limit_side
  and check mesh compatibility
- fix flags unit test
Finish unit tests for FieldSet

- FiledSet unit tests
- add operartor== to FlagArray template
- add limit_side getter to FieldCommonBase
- add stream output operators to FieldCommonBase and FieldSet
- remove FieldSet::flag
- add FieldSet::flag_add
Merge branch '1.8.0_master' into JB_finish_fieldset

Conflicts:
	src/la/bddcml_wrapper.ipp
	src/reaction/dual_por_exchange.cc
	src/reaction/sorption_base.cc
	src/reaction/sorption_dual.hh
	src/system/application_base.cc
	src/system/application_base.hh
Make field_set.cc

- move implementation to separate file
Translate and clean test06 geo fiels
Rename FieldCommonBase

- to FieldCommon
- move it to separate file

after while we want to rename it to FieldBase but not now to
prevent clash with previous FieldBase<> template.