GRID datastructure refacto

[matthieugayon]

the Pattern datastructure is for the moment mapped in a straightforward fashion from the GridPattern struct, because their length is Equal ( NUM_STEPS = 32)

In the future this number may differ, so we need to rewrite the mapping, to adapt to any kind of difference

iced_sequencing/src/core/grid.rs

Line 590 in 93a5289

impl From<GridPattern> for Pattern {

and we need to introduce two new concepts to the grid : editable time signature & granularity (Widest , Wide, Medium, Narrow, Narrowest).

This has several consequences :

• displayed offsets are no longer the one contained in the Pattern datastructure, it's a grid artefact and it needs to be mapped to the granularity
• new move rules
• possibly gate length introduction
• ...