Implement deletion actions and etc.

[wdzhou]

Main

• Close application from menu

GSAS tab (Bragg Peaks)

• Bug fix: in 'multiple GSS' mode, loading a new GSS file results in a blank canvas
• Implement deletion of individual GSAS workspace from GSAS tree;

SofQ tab (Calculate G(R))

• Implement deletion of individual workspace from SofQ-GofR tree;
• Implement deletion of multiple workspaces from main node of SofQ-GofR tree;
• Implement removing one line, G(r) or S(q), from canvas;
• The loaded G(r) from file does not appear in any tree node;

Extra

• Implement a pop-up window to show data in table
• Enable FastGR to read .getN file;