[BETA] v0.9b - Ready to test

Aqara Wireless Smart Light Switch
Models WXKG02LM / WXKG03LM (2016 & 2018 revisions)
Initial beta release v0.9b

This device handler was split off from the "old" Aqara Button device handler in order to best support the two revisions of the one and two-button Aqara Wireless Smart Light Switches. The code has been written so that this device handler can be used with any firmware version, but for users with hub running on Firmware 25.20 or newer, all three actions of the older 2016 revision two-button model WXKG02LM are now recognized: left, right, and both button(s) pushed.

Although this device handler is still considered in beta, it should be fully functional.

initial release notes
* started with v1.3.5 of Aqara Button device handler and removed all references to square Aqara Button
* 2-button model WXKG02LM (2016 revision) - added firmware 25.20 & newer support for all three possible actions: press left/right/both button(s)
* 1-button model WXKG03LM (2018 revision) - completed support for all 3 possible actions: press/hold/double-click button
* 2-button model WXKG03LM (2018 revision) - completed support for all 6 possible actions: press/hold/double-click left/right/both button(s)
* added method imports to match device handlers on GitHub/SmartThingsPublic
* removed unneeded `endpointId` and `profileId` from device fingerprint
* added `ocfDeviceType` to definition in attempt to get device handler working with new SmartThings Samsung Connect mobile app
* added preliminary support for Device Watch
* refactored "raw" read attribute message parse code
* improved identification of model and revision at pairing to correctly set number of buttons available to Smart Apps
* added initial button event for proper configuration during device pairing
* improved followup in `updated()` after user saves preference settings
* added more helpful inline comments to code
* minor code cleanup and reorganization