Add long press actions to undo/redo buttons

[andiandi13]

When we do many modifications on a note, if we want to reset it, we have to press "undo" a lot of times (even hundredths). Plus if we exit the note, it's too late, modifications are saved.

• Long-pressing Undo would undo all modifications, restoring the note to it's initial state.
• Long-pressing Redo will re-apply all modifications to the last one

PS : Action bar buttons (undo/redo and others) don't have a round highlight when we press them, contrary to Formatting actions , which sometimes made me doubt if I pressed undo/redo button. It'd be nice to add that.