Initial commit of removal of double

I'm starting this PR to stimulate discussion of the removal of the use of 'double' in the metadex, to that end i've done three things:

1) changed the types of 'double' in mastercore_dex.cpp to 'cpp_dec_float_50'
2) changed the printf's to display a formatted string from the new type
3) added some casts for calculations that were implicitly casting to an integer

looking forward to the discussion!