[Feature Request] Modules eigenvector determination

[bvenn]

After network modules are identified the 'average signal profile' can be identified by calculating the modules eigengene. It would be a handy addition to investigate the structure of module.

Specifically, we define the module eigengene as the first right-singular vector of the standardized module expression data (Methods, Eq. 29). - Langfelder and Horvath, 2007, BMC

Notes:

• A singular value decomposition is required. Whether a statistics library depedency makes sense is open to debate.
• A standardization may be necessary.
• After that, the eigengene may need to be inverted, depending on the correlations of most of the elements in it.
  • The orientation of the eigengene is solely determined by the orientation of the first row of the matrix