Add D-Bus signals for led pattern active state changes

Emitted when pattern is activated/deactivated within mce.

[mce-headers] Add D-Bus signals for led pattern active state changes
Document tracking id parameter for cpu keepalive method calls

The support for the tracking id parameter was added to mce 1.23.7,
but the documentation was not updated accordingly.

[mce-headers] Document tracking id parameter for cpu keepalive method calls
Merge pull request #5 from spiiroin/add_led_pattern_signals

Add led pattern signals