Update Salt Precipitation Model

[gdfldm]

Update Salt Precipitation Model description in section 1.5. This includes adding a description of the c_w^salt variable - possibly resolving issue #14.

Clearing direct formatting:

1. changed equations from centred to left justified
2. changed formatting of some text in EOR section. I think this has been resolved.
3. seemed to add an extra page at the end of the section (with background image)