Enforce sensible aspect ratio for PCA plots

[lgatto]

Based on feedback from EuroBioc2918:

PCA plots should have 1:1 aspect ratio, and generally be wider (PC1) than high (PC2)

[lgatto]

Clarification - plots should be wider, to account more var explained along PC1.

[lgatto]

This have the feeling that this has worsened with v2 with the left and right side bars.

[lgatto]

ping @lmsimp

[lmsimp]

I can have a look into this again.

The user has the option to hide the sidebars in the dashboard leaving the whole plot space free. So they can have more plot space than in the previous app style.

The motivation behind the sidebars is not to be fancy but make the main plot space cleaner. Unfortunately, in Shiny it’s not trivial to specify fixed elements and to stop elements overlapping with one another eg see this post https://stackoverflow.com/questions/63833695/stop-elements-in-a-shiny-sidebarpanel-from-overlapping-in-columns

[lmsimp]

Only feasible option I see here is to have the plots one above another e.g.

mfrow = c(2, 1)

and then fix the y-axis

[lmsimp]

See https://www.huber.embl.de/msmb/Chap-Multivariate.html

Beware the aspect ratio when plotting a PCA. It is rare to have the two components be of similar norm, so square shaped plots will be the exception. More common are elongated plots, which show that the horizontal (first) principal component is more important than the second. This matters, e.g., for interpreting distances between points in the plots.