Remove "Leve" from "XxxLevelStatistic

Rename PeakLevelStatistic, ClusterLevelStatistic and SetLevelStatistic
in PeakStatistic, ClusterStatistic and SetStatistic
Rename "BetaMap" in "ParameterEstimateMap"
Rename "fileName" in "originalFileName"

as mentioned in issue #48
Update serialisations
Merge pull request #54 from cmaumet/termUpdateFromissue48

Merge: Term updates according to issue #48 (as agreed in NIDASH call)
rebasing
Update sub volume "label" according to "type"
Update serialisations