Tweak option to toggle off visibility of extrapolated f-curves.

Best place for 'Show extrapolation' command with on/off checkbox in the graph editor menu - View.

#### The option ‘Show extrapolation” is ON

Graph editor behavior is as usual. The option is ON by default.

#### The option ‘Show extrapolation” is OFF:

Then:

- Constant extrapolations are hidden.
- Linear extrapolations are shown.
- Cycle modifier present but set to No Cycles: see above.
- Finite cycles are shown. Beyond the cycles: see above.
- Infinite cycles are shown.

If the extrapolation part of the curves are shown they should be drawn a bit different (lower opacity or dotted) whether show_extrapolation option On or Off.

Single keys. They should be shown just as single keyframes in the graph.

##### But first of all we have to implement the simplest variant

###### The option ‘Show extrapolation” is On: shows extrapolated curves.

###### The option ‘Show extrapolation” is Off. doesn't show extrapolated curves at all, whether it is a cycle, a linear extrapolation or a constant.

Examples:

###### And this are examples for possible improvements on next possible upgrades:

Constant extrapolation:

Linear extrapolation:

Cycle extrapolation finite:

Cycle extrapolation infinite: