Restore GUI state of Grapher View

[stefanhahmann]

User Story

Currently most of the windows that had been open, when a Mastodon project was saved a restored in the state as they were, when the project is opened again. This is a really nice functionality.
However, the grapher view is not completely included in this process. I would like that the following things are restored, when a Mastodon project is opened:

• Selected Feature for X axis
• Selected Feature for Y axis
• Choice for Items to plot
• the context in case the choice for items to plot is From context:
• Whether or not show edges is checked
• The axes scales at the time of saving the project

Also I would like the Grapher to perform a plot with the restored settings. All this together would make the Grapher look as it was, when the project was saved.

[tinevez]

Fixed via #344