feat(hud): add possibility to specify a hud image in block based api

closes #17
Merge pull request #19 from michaelochs/feature/#17-HUD_image_in_block_based_api

feat(hud): add possibility to specify a hud image in block based api
Merge branch 'develop' of https://github.com/michaelochs/BCScanner into develop

Conflicts:
	Example/BCScannerExample/MainViewController.m