Fix stdin control in absence of dbus

## Rationale

Allow keyboard control via STDIN even in absence of dbus. Very important for headless server Pis, used also as media centres. Quick merge and release would be greatly appreciated.

## Changes

Keyboard:
Keyboard reading fully functional even in absence of dbus.
Store last keystroke in member m_action.
New method getEvent() returns and clears it.

OMXControl:
init returns error code -1 if dbus connection fails.

omxplayer:
If OMXControl failed to connect to dbus, read keystrokes directly
from Keyboard::getEvent().

Fixes #62
Fixes #131