[OGUI-1863] Add dropdown with multiple save root as image extensions

[hehoon]

I have JIRA issue created

• branch and/or PR name(s) includes JIRA ID
• issue has "Fix version" assigned
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Changes:

• Changed the "download root as PNG image" to a dropdown
  • The dropdown contains buttons to save the root as an image for multiple filetypes
• Moved SUPPORTED_ROOT_IMAGE_FILE_TYPES to a seperate enum file
• Added simpleDebouncer to the global utility file and removed the unused function getFileExtensionFromName
• Added an "extra object data" attribute to QCObject, so extra data about an object can be stored (in-memory)
  • This is currently only used to know whether the toolbar of a plot on the layoutShow page should remain visible.