Added exception raising if linux user does not have permission to work with camera
Updated Display.py with pressed feature enabled

It is with reference to issue no 120
https://github.com/ingenuitas/SimpleCV/issues/120
Fixes typo from commit which fixed typos

Fixes typo in #399
Uhg camera permission checking breaks stuff
TravisCI should be happy now
added motionBlur for images
test coverage increased, 0 intensity catched
Small changes in VirtualCamera

Was supposed to fix #135, but #407 already does it. However, making things
more pythonic is always worth it.