Store Dim Level When Resume Dim is Enabled

[krkeegan]

Is your feature request related to a problem? Please describe.
Resume Dim as added by #411 alters the default on_level of devices. However, the on_level is not stored, so when the device is toggled manually, it reports 100% brightness when it may be less than that.

Describe the solution you'd like
I think the solution needs to look something like

Add logic to the handle_on_off method in Device/base/Base that saves the on_level when resume_dim is enabled. This can be saved to set_meta("on_level"), which is already used by the local_on_level setting, to enable it to work across reboots. This will require saving the resume_dim state to the meta field and then checking this state inside handle_on_off

Then when derive_on_level in DimmerBase is called it will report the correct on level.