[FEAT] Horizontally stacked boxpoints

[carrascomj]

Closes #47.

Description

Add the ability to have more than one boxpoint per arrow and condition, stacking them horizontally. This allows the representation of isozymes.

Text tags are added as appear in the data to indicate the particular variant and the horizontal alignment is shared across conditions.

Grammar of graphics

A new aesthetic was introduced to indicate the variable that controls horizontal stacking: stack. y would have been also a good choice but, since it will always clash with the hist/kde y (since they require different types), it was avoided.

ggshu(df, aes=aes(stack="isozyme", color="enz_concentration")) + geom_boxpoint()

Implementation

• src/data.rs: A new optional Data input field is accepted for metabolism input. This triggers the generation of boxpoint Aesthetic entities with a new component that indicates the horizontal index and the name (sharing order with the reaction identifiers).
• src/aes.rs and src/funcplot.rs: boxpoints can add different boxes per arrow in the x-axis (condition-wise as before) and now also in the y-axis (box_variant-wise).
• src/aes.rs: Text2d tags are spawned together with each box per condition and variant.
• ggshu: the new aes was added to geom_boxpoint, with its corresponding data handling.