sort ds_list to ensure velocity as first and residue/intercept as last

[yunjunz]

Description of proposed changes

• add utils.readfile.sort_dataset_list4velocity() to ensure velocity are the first dataset, and intercept/residue are the last datasets. This fixes the behavior change introduced in ts2vel: save residue & intercept #835, as reported by Sven in the user forum

• tests/smallbaselineApp: use *.tar.gz file, in addition to *.tar.xz file, if exists.

• add mintpy.objects.progress.FileProgressObject class to show a progrerss bar during uncompressing

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