Modularize core

[eweitz]

This reduces Ideogram.js's core module from ~2800 lines to ~200 lines. The new highly modular core -- now restored to its original name, ideogram.js -- consists of a simplified constructor method and several small static methods. All instance methods have been moved to new modules:

• annotations.js
• bands.js
• brush.js
• coordinate-converters.js
• init.js
• lib.js
• services.js
• sex-chromosomes.js

Refactoring the massive core module into 8 smaller modules significantly improves maintainability.

[coveralls]

Coverage increased (+0.3%) to 91.244% when pulling 7922e8c on modular-core into d098689 on master.