Added new methods to ExecutableModel interface to access floating amount and compartment init values.

New opiton to load model enum to enable / disable mutable initial conditions.

Added function pointers to LLVMExecutableModel for setting init conc and comp volumes.

New fields to LLVMModelData to indicate length of init cond arrays.

Pick out independent and dependent init conditions in LLVMModelDataSymbols.

fill init conditions map for compartments.

code generator for set comp init conditions.
ran osx tests