Set the default constituents value for species until the CAM-SIMA file I/O object is ready

[boulderdaze]

Set the initial constituent values for species upon instantiation, until CAM-SIMA has file I/O available to provide the initial constituents for the species.

Add the entry in the chemistry data to read the initial values.

__default value (mol mol-1)": 4.3e-6

[boulderdaze]

This doesn't need anymore since the PR in CAM-SIMA removed default value constituent overwrite