Added Network Support to SEAHORSE

[taraeicher]

Added support for associations between phenotypes and network features, supporting both binary and continuous features. Statistical models used are as follows:

• Continuous feature, continuous phenotype: correlation
• Continuous feature, nominal phenotype: ANOVA
• Continuous feature, dichotomous phenotype: Welch's t-test
• Dichotomous feature, continuous phenotype: Welch's t-test
• Dichotomous feature, nominal phenotype: Chi-square or FFH
• Dichotomous feature, dichotomous phenotype: Chi-square or FFH