cmake: do not cache libusb library if libusb-1.0 headers not found

Library found might be an older libusb version.

Closes #158
Allow disabling PROTOBUF support

One dependency less for users that only use DISPMANX grabbing
Fix linking with static Qt Embedded builds

Make sure pthreads and dl get linked when building Hyperion
using a static Qt Embedded library instead of Qt X11
Merge pull request #159 from maxnet/master

Misc build improvements
Merge pull request #165 from kammerjaeger/master

Support for WS281b
Added missing include
Minor reformat of code to match hyperion-style. Added ws2812b as option to disable for devices without dma-pwm
Updated binary-release
Started on adding a configurable delay in case leds are ahead of picture
Set the DMA ws2812b to default OFF in build
Added black color before boot-sequence, to make sure that the boot-sequence is the first thing to start
Updated RPi release
Added delay to smoothing and changed the switch off to continue sending black
Added some code comments
Added debug statement to standard out
Updated RPi release
Created a preliminary binary release for the HummingBoard (or cubox)
Merge remote-tracking branch 'origin/master'
Updated the HummingBoard release
Updated proto-definition due to changes in newest protobuf library