Graphs support is broken in many places in UGENE

After refactoring done in 2013-2015 graph support is broken:

1) Graph calculation in separate thread is not thread safe. Calculation of the graph with multiple series have a high chance of crash (try toggle GC Frame Plot on sequences > 1mb)

2) Min/max (extremum) values for labels are wrong.

3) Graph color dialog is not shown if there is at least 1 label on the screen (checked on Linux only).

4) Labels can't be toggled in reliable way.

5) Cutoff related code sometimes use only maximum values and ignores minimums.

6) On screen pixel offsets sometimes are used in place where sequence offsets should be used.

7) Sequence offsets sometimes are used where graph data point indexes should be used.

There are many other issues. The code should be cleaned up and re-tested again.