Updates Set methods in ScalarFields

[shishiousan]

I think this issue is strongly related the issue number #179

When a ScalarField_ is set by the addContribution=.FALSE. and given scale value, it does not work properly.

For example:

CALL obj%set(VALUE=avec,  &
      & addContribution=.FALSE., &
      & scale=alp)

currently, performs following operations.

obj = obj + alp * avec

But, it should perform following:

obj = alp*avec

[vickysharma0812]

ScalarField (and other fields) under the hood use routines from base library (see RealVector_SetMethods module).

As @shishiousan San suggested, we can make an internal copy called alpha * value and call the current Set method. But, I do not recommend this, because we have to repeat this for other fields, in addition, we make additional copy to store alpha * value.

Therefore, we should add optional argument in the Set method defined in RealVector_SetMethods.

Regards
Vikas