CCB's preview image generated with the resolution set now.
Bugfix for #458 New CCB files takes several seconds to appear in resources list.
New method added to update the resource manager immediately for a given filename.
Triggers updating the resource manager upon creating a new file.
Bugfix: #302 Sprite sheet preview images not updated correctly.
Existing images were not overwritten.
Added logging of error messages.
Refactoring: Extracted method for preview image generation.
Refactored/Cleaned up SnapLayer
Modified ruler png to be white so can be colored in code.
Merge pull request #480 from cocojoe/develop

Refactored/Cleaned up SnapLayer
Merge pull request #474 from NickyWeber/bugfix/#458_slow_appearance_of_new_ccb_in_resource_list

Bugfix for #458 New CCB files takes several seconds to appear in resourc...
Merge pull request #478 from NickyWeber/bugfix/#302_spritesheet_previews_not_updated

Bugfix/#302 spritesheet previews not updated
Merge pull request #473 from NickyWeber/bugfix/#416_preview_images_screwed

CCB's preview image generated with the resolution set now.
Merge branch 'develop' of https://github.com/apportable/SpriteBuilder into joints2