Updates to valiDrops

[Sandman-1]

• Fixes breakpoint error typo when ranking barcodes
• Allows autocalculation of segmentation parameters with seg.control function
• Permits modification of values for h, maxit.glm, and tol within seg.control function for all steps of pipeline
• Fixes rare error on expression metric calculation by limiting deep clustering resolutions if necessary
• Added optional time limit for each stage of pipeline
• Allows user to terminate pipeline if more than twice as many barcodes are retained after ranking and QC filtering (prior to calculating expression characteristics) as in the default filtered matrix generated by alignment software, e.g., Cellranger, CeleScope, etc.