a3d1 import fixes

[davidejones]

Instigated from issue #3 This PR fixes some issues with importing a3d version 1 files.

• Sets the default type for name on a3dobjects as string
• Reads the mask for visibility values, not sure why this was skipped perhaps as i didn't have a file spec for v1
• Fix error embedded null character when loading images on newer versions of blender
• Use object names when converting a3d1 to 2, previously used the same name for all due to a bug
• Fix export bugs with texture material accessing params that don't always exist