Add an ability to copy the value from Observable without having to access it first

[Mattijah]

Currently when copying values (let's say between models), we always need to access them.

Example:

model.name.value = diffModel.name.value
model.name <- diffModel.name.value

// or shorthand
model.name <- diffModel.name^

The improvement allow use to do this:

model.name <- diffModel.name

There is no need to access the value of the Observable and since we use <- operator this action seems to be also pretty clear (unlike =).