Add arrows

[lpatiny]

Currently it is possible in the SvgRenderer to highlight some bonds and atoms.

Internally it use 'useHighlight' in order to change the style.

We would need the possibility to annotate the molecule using 'arrows'.

This means:

• SvgRenderer (and also SmilesSvgRenderer, IdcodeSvgRenderer and MolfileSvgRenderer) should allow a new property 'arrows'
• arrows is an array of object that contains 'atom1', 'atom2' and svg 'style' property (allows to change color, thickness, from, to), 'kind' (either a straight 'line' or 'curved' (an arc) , default 'line')

The coordinates of the center of the atoms can be found by searching the resulting SVG for the corresponding id and searching the cx and cy properties like in :

Once you have based on atom1 and atom2 the from / to of the arraw you should add it in the renderer

New properties in the storybook should be added in order to debug / test this new feature.

NB: Many arrows can be added at the same time