Merge pull request #22 from agbeltran/dev

'correlation coefficient' restrictions
changing curation status for one tail, two tail test, completing statistical inference class definition, closes #12
adding covariance, closes #14
adding design matrix and constrast, closes #9
recasting 1 and 5% fdr as instances, not classes, closes #24
clarifying the different t-tests making the original student t-test a defined class under which all other t-tests classify (dropping the original objective from that class), adding 3 classes and relevant metadata, correction to distribution used in paired t-test, adding a 4 subtypes of contrasts (but more work is needed with respect to parameter and parameter estimate discussion and distinction between contrast vectors or contrast estimates), adding restriction on one/two tail test so they classify under statistical tests
minor edits to z-score and restrictions on measurement data item subtypes about data set or proba distro
adding missing definitions where applicable: 4 classes in this action: STATO_0000207, _0000288,_0000158,_0000223
adding defintion on STATO_0000146
adding definition to STATO_0000034
adding definition to STATO_0000258 variable and STATO_0000002 file
adding placeholder definitions for random, fixed and mixed models, more work is needed
minor edits
changing label of class file
adding definition to STATO_0000081
Changed label from 'association testing objective' to 'association between categorical variables testing object', added textual definition for 'genetic association study' and added restriction to 'Person's chi square test'
splitting Pearson test in 2 distinct classes, creating Barnard test, setting restrictions, assigning stato id to new classes
creating 3 new classes for CCD, PB and BB designs, metadata complete, possibly more work on formal definitions
fixes to definitions: anova and subtypes, a number of plots, NOTE: anova definition has been modified but anova is an import from OBI which requires attention
adding synonym to U-test