Add progress reporting during clustering

[mlinderm]

Add progress reporting during clustering to give the user an indication that SPADE is still working. Specifically provide an estimate of percent completion.

[mlinderm]

Example output:

Loading required package: igraph Loading required package: methods Scalable Robust Estimators with High Breakdown Point (version 1.3-01) Downsampling file: ./SimulatedRawData.fcs Clustering files... Estimated clustering progress: 0% ... Estimated clustering progress: 8% ... Estimated clustering progress: 16% ... Estimated clustering progress: 24% ... Estimated clustering progress: 33% ... Estimated clustering progress: 41% ... Estimated clustering progress: 49% ... Estimated clustering progress: 57% ... Estimated clustering progress: 100% Upsampling file: output/SimulatedRawData.fcs.density.fcs Computing medians for file: output/SimulatedRawData.fcs.density.fcs.cluster.fcs

Note that the progress is a crude estimate as the number of clustering rounds is highly data dependent.