Add keyboard shortcuts to grid

[erickgomez28]

For navigation on the main grid or in the subgrid of a selected area:
Arrow right: move the hover to the right cell
Arrow left: move the hover to the left cell
Arrow down: move the hover to down cell
Arrow up: move the hover to up cell

In addition to its current functionality:
Esc: cancels the edit column or row name separator
c: add a column where I have the hover
r: add a row where I have the hover

New Actions:
Espace: select an area to edit or select an empty area to create
Shift + c: remove the column from the current hover cell
Shift + r: remove the row from the current hover cell
Shift + g: clean the area if it has a subgrid
Ctrl + c: copy the generated ccs code

This can be other PR:
Shift + arrow right: select column separator right
Shift + arrow left: select column separator left
Shift + arrow down: select row separator down
Shift + arrow up: select row separator up

When the row or column separator is select:
Espace: edit separator name
Arrow right: add width to the column left and remove width to the column right
Arrow left: add width to the column right and remove width to the column left
Arrow down: add height to the row up and remove height to the column down
Arrow up: add height to the row down and remove height to the column up

[erickgomez28]

Hi @matias-capeletto, these are my suggestions to expand the current keyboard shortcuts.
What do you think?

[patak-dev]

I think these are great additions. I really like the idea of add columns and rows where you are. I think we may need to see it work to fine-tune it, but let's try!

@agustin-capeletto-lenio what do you think about shift+click for deleting rows/columns?

About the shortcuts when you are in a line, I think they are nice to have. I am only afraid about how we people are going to discover all these keyboard shortcuts. We may need to have a help button with an explainer for all of them.