Add plugin for enabling/disabling doubletap wakeups

After doubletap enable/disable controls are defined in mce ini-files,
the doubletap wakeups can be configured to be
- always enabled
- always disabled
- enabled when proximity sensor is not covered

[mce] Add plugin for enabling/disabling doubletap wakeups
Support query/change of doubletap wakeup settings

New mcetool option added
  -z, --set-doubletap-wakeup=<never|always|proximity>

[mcetool] Support query/change of doubletap wakeup settings
Report proximity not covered if sensor disabled / not available

If no usable proximity sensor backend if found, or if the use of
proximity sensor is disabled via runtime configuration, the proximity
plugin will report that proximity sensor is not covered. This is needed
to keep unrecoverable proximity blanking from occurring.
Tone down logging level
Merge pull request #102 from spiiroin/doubletap_plugin

Add plugin for enabling/disabling doubletap wakeups