`spm:contrast` => `nidm:ContrastEstimation`

As currently discussed in issue #36.
No standard error map natively in SPM

`spm:standardError` deleted to keep only
`nidm:contrastStandardErrorMap` as `prov:type`
Rename `clusterLabels` in `clusterLabelsMap`

To emphasise that this attribute is a `Map` as in `statisticMap`,
`contrastMap`, `betaMap`...
`nidm:Inference` activity in `nidm` namespace

`spm:Inference` => `nidm:Inference`
Rename `nidm:labelId` in  `nidm:clusterLabelId`
`pValueFWER` and `qValueFDR` in `nidm` namespace
`softwareRevision` in `spm` namespace
Replace `statisticType` by `prov:type`

As suggested in NIDASH-DDWG call 7/04/2014.

- For each statistical map defines a second `prov:type` attributes to
specify the type of statistic in use. In this example for t-test we
have:
prov:type = 'nidm:tStatisticalMap'
- For each contrast defines a second `prov:type` attributes to specify
the type of statistic in use. In this example for t-test we have:
prov:type = 'nidm:tContrast'
Replace `statisticalTest` by `prov:type`

Similarly to what was done to delete the `statisticType` term.

- For inference defines a second `prov:type` attributes to specify the
type of test in use. In this example for a one-sided we have:
As suggested in NIDASH-DDWG call 7/04/2014.

- For each statistical map defines a second `prov:type` attributes to
specify the type of statistic in use. In this example for t-test we
have:
prov:type = 'nidm:tStatisticalMap'
- For each contrast defines a second `prov:type` attributes to specify
the type of statistic in use. In this example for t-test we have:
`prov:type = 'nidm:tContrast'`
Replace `subVolumeMask` by `maskMap`
Rename `spm:estimation` in `nidm:ModelFitting`
`userSpecifiedThresholdType` in `nidm` namespace
Capitalise `Spm`
`excursionset` in `nidm` namespace
`clusterLevelStatistic` in `nidm` namespace
`peakLevelStatistic` in `nidm` namespace.
Activities: Model fitting & Contrast estimation
Update according to terms spreadsheet
Add: z-stat map
Add: contrast variance map