Adjust display linger times after ending a call

When call ends the linger time specifies the length of time during
which the display will turn on / stay on if proximity is uncovered
before previous display state and normal blanking policy is restored.

For incoming calls the linger time should be long enough to allow the
user to select "call again" or similar continuation actions. For now
5 seconds is used.

For outgoing calls the linger time should be long enough to allow the
user to remove the device from ear. For now 2.5 seconds is used.

[mce] Adjust display linger times after ending a call. Fixes JB#20810
Blanking inhibit mode is evaluated also during call

If automatic blanking is disabled, it should stay disabled also
during active call.
Do not turn display on after linger time if proximity sensor is covered

Also, unless the display was clearly on when the the exceptional
situation started, the display is turned off after linger time.
Merge pull request #186 from spiiroin/end_of_call_linger

End of call display linger