Update terms to be consistent with Terms spreadshhet

Update terms voxelToWorld, pValueUnc, pValueFWER and equiv_Z-statistic
into voxelToWorldMapping, pUncor, pFWER and EquivZstat to be consistent
with the terms defined in the Neuroimaging terms spreadsheet.
Updates suggested by Nolan
Merge pull request #5 from cmaumet/master

Update terms to be consistent with Terms spreadsheet