N2 toolbar buttons added to access collapse/expand and variable filter modes

[tadkollar]

Summary

Previously, the only way to expand/collapse nodes in the N2 diagram was to right-click, and the only way to filter component variables was to alt-right-click. To make those functions more obvious and provide an alternate interface when certain browsers male this difficult, buttons were added to the toolbar. Each of these toggle a mode where the associated function is activated by left-clicking a node in the diagram.

The following changes were made to the diagram:

• The help and legend buttons were combined into an expandable group at the bottom of the toolbar
• The N2Click class was added to manage changing to or from one of four modes (normal, node info, expand/collapse, variable filter). Previously, only the normal and node info mode had to be managed
• Two new button icons were created
• The info mode button was combined into an expandable group with the two new buttons
• The help screen was updated to fit all of the content in the window
• Tests were modified/added to accommodate the new design
• An existing issue was found and fixed in the toolbar where for some expandable groups, clicking the root button would copy its image to the wrong group

Related Issues

• Resolves Add a tool to expand, collapse, and select variables in the N2 diagram #2345

Backwards incompatibilities

None

New Dependencies

None

[coveralls]

Coverage decreased (-0.3%) to 89.402% when pulling be977e5 on tadkollar:varbtn2345 into f47eb54 on OpenMDAO:master.