[IMP] web_editor: handle advanced table edition

[Zynton]

This adds many improvements to table editing in Odoo Editor, as well as some styling improvements.

New features :

• Rectangular cell selection
• Changing the color of a cell
• Buttons to add/remove/move rows/columns
• Resize rows/columns

task-2858455

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[robodoo]

Pull request status dashboard.

[dmo-odoo]

This PR adds quite a lot of loc that are extremely specific to tables. Maybe we should explore options to separate them into different files ? It can be done post merge but I think you know what I mean. It would be great to have all things related to tables inside one or multiple files that only handle specific table behaviors.

[Zynton]

@dmo-odoo Done! I made some of the changes discussed in new commits and squashed what should be squashed.

[dmo-odoo]

@robodoo rebase-merge r+

[robodoo]

Merge method set to rebase and merge, using the PR as merge commit message.