Added minimal coverage support.

First version of coverage model.
3DV: Added business support to central track.

next is visual support
Added drawing support to central track.

next: bug fixing.
3DV: minor bug fixing. Good presentation commit.

TODOs: color interblending of central track. Improve coordinate input,
with nucleotides instead of [0,1] coordinates.
3DV: minor bug fixing. Related to data storing.
3DV: Added GUI support.

Added different mouse tools.
Improved region handling.
Improved selection.
3DV: added alignments rendering.
3DV: Improved performance and scale awareness.
Added alignment rendering support.
3DV: Alignments demonstration commit
3DV: Added Leap support.
3DV: Fixed bug.
3DV: improved coverage asynchronous load.
3DV: Improved asynchronous load.

Revision used in demonstration.
Merge branch 'develop' of https://github.com/opencb/jsorolla into develop
Fixed bug.
Created indexedDB-store.
Developed IndexedDB.
Asynchronized FeatureChunkCache.

Last commit backwards compatible.
Refactor adapters to use async API from FeatureChunkCache.