Use sigmal clipping when focus frames count > 3 and simple averaging for the...

Use sigmal clipping when focus frames count > 3 and simple averaging for the rest. Please note that invalid values for currentHFR (-1) must be counted and passed to the focusing algorithm since it is responsible for making decisions on how to correct this.
Also using read-only QLineEdit instead of QLabel because it looks better and users can copy the current absolute position from it.

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