Fixed Excel Export #919, #907

Export to Excel works completely for all accepted sheets. See #919 & #907 for further information

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

dondi / GRNsight

Fixed Excel Export #919, #907 #920