Add nicer way of specifying datatype

[moble]

Currently, certain vector variables need to be added with code specifying

dataype='std::vector<double>'

for example. There are similarly complex quantities that are added with

dataype='std::complex<double>'

I should just create strings somewhere like

vectorType = 'std::vector<double>'
complexType = 'std::complex<double>'

so that I can add those variables with code specifying

datatype = vectorType
datatype = complexType

Thus, if anyone wants to change the type, they just have to do it in one place.

Alternatively, just make separate functions for, e.g., AddDerivedComplexConstant.