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
Update README.md
Update README.md
Update README.md
Merge pull request #5 from cmaumet/master

Update terms to be consistent with Terms spreadsheet
Use coordinateSystem

Replace `nidm:coordinateSpace = "MNI"` by `nidm:coordinateSystem =
'nidm:mniCoordinateSystem'` for consistency across the document
fix: add missing fileName and voxelToWorldMapping

Add `nidm:fileName ` and `nidm:voxelToWorldMapping` in entities
`niiri:search_space_id` and `niiri:excursion_set_id`
fix: add missing label in peaks and coordinates
fix: add location, fileName and voxelToWorldMapping

add `prov:location`, `nidm:filename` and `nidm:voxelToWorldMapping` to
store full path, file name and voxel-to-world matrix respectively and
remove `prov:value` in `niiri:statistical_map_id`,
`niiri:contrast_map_id`, `niiri:search_space_id`,
`niiri:excursion_set_id`
fix: add contrastName

Add `nidm:contrastName` in entity `niiri:statistical_map_id` and
`niiri:contrast_map_id`
fix: two terms for degrees of freedom

Create two attributes `nidm:errorDegreesOfFreedom` and
`nidm:effectDegreesOfFreedom` instead of a single attribute
`fsl:degreesOfFreedom`
fix: move reselSizeInVoxels

Moved `fsl:reselSizeInVoxels` from `niiri:stat_image_properties_id` to
`niiri:search_space_id`
fix: delete stat_image_properties

Removed `niiri:stat_image_properties_id` entity.
fix: delete cluster_level_id and peak_level_id

Removed `niiri:cluster_level_id` and `niiri:peak_level_id` and
connected directly clusters `niiri:cluster_XXXX` to excursion set
`niiri:excursion_set_id`.
fix: hadMember replaced by wasDerivedFrom

Changed `hadMember` relationship by `wasDerivedFrom` when connecting
two entities.
fix: delete featVersion

Removed `fsl:featVersion` in entity `niiri:software_id`
fix: coordinates as prov:location

Coordinate defined by `prov:atLocation` in peaks.
fix: delete contrastVector and designMatrix

Remove `fsl:contrastVector = "1.000000 0.000000"` and `fsl:designMatrix
= "designMatrix.png"` from entity `niiri:contrast_map_id`
fix: add label

Change `fsl:label` into `prov:label` and add a `prov:label` attribute
in each entity.