funcalign: Add cumulative variance explained for SRM

[qihongl]

Hi, can we add a cumulative variance explained function for SRM?

I guess this feature is not in the SRM implementation because this calculation involves fitting SRM with different numbers of components (like this)? So it seems to be a util kind of function... Or is there a faster way of calculating cumulative variance explained by different numbers of components?

[qihongl]

If this is what we want, should I try to implement it in the util module?

[mihaic]

I think adding an implementation would be great. Probably it should be in funcalign if it only applies to SRM, though.