update images & outdated info

[thao-do]

Purpose

Fix images that were still not loaded correctly in the doc and edited some outdated info resulted from the last few rounds of plugin rc version updates

Changes

Updated images:

• Fixed incorrect image file names
• Add a figure directive to show an existing screenshot image (Tab_thresholding.png) that was supposed to show in the Thresholding step
• Added a new screenshot to the last step of Thresholding

Updated info:

• Remove mentions of "Time out" and "Cancel"
• Thresholding section had missing steps here and there --> edited for correction & clarity

Testing

• All changes were reviewed in a local build.
• Images were checked to be existed in the appropriate directory.

How to review

• Review text changes