hicAdjustMatrix new mode: `keepByMasking`

`hicAdjustMatrix` is currently removing bins when `--action keep` is specified. If someone uses a BED file of many regions within a chromosome, the adjusted matrix plotting is broken.

Therefore, `hicAdjustMatrix` should have 4 modes:

```
keepByMasking
keepByDeleting
removeByMasking
removeByDeleting
```

Although I'm not sure that `keepByDeleting` has many interest.