Fix stdin control in absence of dbus

## Rationale

No STDIN w/o DBUS seems to be a showstopper for a few people.

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