Added undo button after draw button in toolbar

[adinlead]

1. Enlarged the delete button icon
2. Added open-source redo and undo icons (from Bootstrap)

[cloudkucooland]

Looks good to me. @le-jeu can approve

[le-jeu]

Thank you for your contribution. I'll give a look as soon as I'm able to.

I will rebase your PR on the dev build from the github interface (unless you do it first).

[le-jeu]

The redo icon is not used.
Could the undo button be disabled/grayed when there is nothing to undo ?

[adinlead]

The redo icon is not used. Could the undo button be disabled/grayed when there is nothing to undo ?

This is a good suggestion, currently there is no such design available
I will try to implement it later, please wait a moment

====================

• When unable to undo, disable undo button

[le-jeu]

The redo icon is not used.

In fact, according to analytics, the redo feature is not used that much so I think we don't need a button for it.
Either way, I'm not sure about the button design as it's more like a play backward button than an undo icon that uses to look as a curved left arrow.

You may also remove the debug/console.log lines