`selector` should accept integers and strings, for all functions accepting the `selector` argument

[nicholas-esterer]

Example functions are update_trace, for_each_shape, etc.

If the selector keyword argument is an integer, it should behave as follows:

• If row and col aren't specified, it should act as an index into fig.data, i.e., fig.data[selector]
• If they are, then it acts as an index into the objects on that subplot, e.g., list(fig.select_traces(row=r,col=c))[selector])

If the selector keyword argument is a string, it should create a dictionary whose sole key is type and selector is the value at the key, e.g., if type(selector) == type(str()): selector = dict(type=selector).