Issue #917 GRNsight should read and retain all network sheets

[Onariaginosa]

Implements changes requested in issue #917

Changed warning intro to tell the user that the file may not export properly. ( #884 )

Pull Request Checklist

• [x] Travis C.I. build passes
• [x] All four Demos look as expected when loaded
• [x] Reload works as expected
• [x] Loading file with Error brings up error modal, and it looks as expected
• [x] Loading file with Warning brings up warnings modal
• [x] Import works for both SIF and GraphML
• [x] Graph can be exported to SIF and GraphML
• [x] Print works as expected
• [x] Restrict graph to viewport works as expected (check/uncheck)
• [x] Viewport Size Changing works as expected (small/medium/large/fit)
• [x] Toggle between Grid Layout and Force Graph Layout works as expected
• [x] Force Graph Parameter Sliders change the number above them and have an effect on the graph
• [x] Locking/Unlocking/Resetting/Undo Resetting the force graph parameters works as expected
• [x] Enabling and disabling node coloring works as expected
• [x] Node coloring options work as expected (selection top/bottom dataset, averaging values, changing max value)
• [x] Weighted graph loaded with the "default to black edges" option checked appears as expected
• [x] Hide/Show Weights works as expected (always/never/upon mouseover)
• [x] Edge Weight Normalization Factor can be changed (set/reset)
• [x] Gray Edge Threshold can be changed, slider changes the number and has an effect on the graph
• [x] Checking Show Gray Edges as Dashed works as expected (check/uncheck)
• [x] D-pad left/right/top/bottom/center works as expected
• [x] Zoom slider changes number and has effect on graph (viewport and menu)
• [x] Right click on a node opens gene page, page is populated with correct data

[ahmad00m]

@ahmad00m has gone through the checklist and found no issues pertaining to any of the checkboxes.