make integration.type parsing conditional on TimeIntegratorOption

[jackieyao0114]

Right now integration.type is mandatory for all values of TimeIntegratorOption.
However, integration.type is only needed for TimeIntegratorOption = 4, not for TimeIntegratorOption = 0; 1; 2; 3.
We should find a way to change the parsing conditional, i.e. integration.type is still mandatory (parsed by get function) when TimeIntegratorOption = 4, but is not required when TimeIntegratorOption = 0; 1; 2; 3. Better off, when TimeIntegratorOption = 0; 1; 2; 3 but there is some integration.type value provided by the input, the code should generate a warning.