Fixes [#5]: Incorrect bone names when prefix removed

[rassweiler]

• Set default hip bone name to Hips
• Pass remove_prefix value through functions
• Use the name_prefix + hip_bone_name to address hip bones
• If remove_prefix is true then set the name_prefix to an empty string

[rassweiler]

Tests Done:

• Importing array of mixamo armatures without root or prefix renaming
• Importing array of mixamo armatures with root and no prefix renaming
• Importing array of mixamo armatures without root and using prefix renaming
• Importing array of mixamo armatures with root and prefix renaming
• Importing array of mixamo armatures with delete armatures enabled