Local BAM files

Nobody has claimed this yet.

```

BAM Files
---------

View sequencing read mappings. First we must load the `higlass-pileup plugin track `_
as a ``hg.PluginTrack``:

.. code-block:: python

%%javascript

require(["https://unpkg.com/higlass-pileup/dist/higlass-pileup.min.js"],
function(hglib) {

});

And then we can view pileups:

.. code-block:: python

import higlass
from higlass.tilesets import Tileset, bam
from higlass.client import Track, View

filename = '../data/ont.10K.bam'
indexfile = '../data/ont.10K.bam.bai'

bam_ts = bam(filename, indexfile)

display, server, viewconf = higlass.display(
[View([
Track('top-axis', height=20),
Track(track_type="pileup",
position='top', tileset=bam_ts, height=50 )
], initialXDomain = [
0,
2000
])]
)
display

.. image:: img/jupyter-pileup-no-code.png

```

Usage of the BAM files is shown in the plugin documentation, but we don't currently support local files and would need to extend the server.

Read the higlass-pileup plugin documentation and compare its BAM example with the Python `bam(filename, indexfile)` usage shown here. Then trace the server extension needed for local files; done means the local BAM and `.bai` example renders a pileup as shown.

Written by the indexing model from the issue text.