Make switch thumb templatable, Add indeterminate state.

[desig9stein]

Describe the solution you'd like

Thumb:
I would like to be able to add an icon inside the switch thumb that further describes the state of the switch.
I should be able to change the icon for the different states of the switch.

Indeterminate state:
According to material guidelines, "because a switch shows the actual status of something, sometimes there is a delay in its change of state. In such cases, a processing status animation can be used".

[desig9stein]

After some further investigation, we decide that there is no need to add an indeterminate state.
Also, we decide not to make the thumb template due to his different sizes in different themes.