update to version 2.2.1

[LinkunGao]

• Modified arrow keys (up & down) to change slices, there are no bugs when using this function.
• Fixed bug: Slice index number not matched between top description area and slider bar area.
• Fixed bug: The image sometimes would disappear when selecting/unselecting contrast checkboxes.
• Fixed bug: Missing slices issue
• Rename cursor to cursor icon and move to the top, In GUI.
• Solved issue: Slice space index issue on threejs environment.
• Solved contrast order issue: the contrast order: Pre-contrast, post-contrast1, post-contrast2, post-contrast3, post-contrast4
• Remove the show contrast button on GUI
• There are only have 5 ( Not hard code, it is based on how many files you uploaded/sent!!! ) buttons to allow users to select which images to show
• Update the information on the intro panel.
• Add Cursor Inspector function, as for how to use it:
  • Press s on the keyboard to enable/disable, then left-click on images, and use the bottom tool’s bar to switch the image orientation.
• Modified the Cursor Inspector function, there are no bugs.