Tabulate filtered genome annotations

[eweitz]

This enables getting Ideogram annotations after filtering, via ideogram.filteredAnnots.

You can then present faceted genome search results in a table. Once there, users can sort and search the dynamically refined features -- e.g. gene lists, variant lists.

The new "Differential expression of genes" example shows this new filtering, tabulating, searching, and sorting in action for NASA GeneLab data on how outer space affects gene expression in muscle.

[coveralls]

Coverage decreased (-0.3%) to 90.55% when pulling 3b541c4418003e8fbeae35d9706e4a7e388f2167 on filtered-annots-table into 3dfabe36252d82b974787945f4425fc6d3b98511 on master.