Move FCE data to the datasets directory

* Removed the FCE attribute from carrier documents, and moved it instead to datasets/:region/fce/:carrier.yml, permitting each region to have it's own FCE profiles. See quintel/atlas@fb06006f. This fixes #708.

* Inputs which use `FCE_START_VALUE` have been modified on account of the function now returning a share instead of a percentage. See quintel/etengine@dc8a9d8f.