Disable memory initializer until the proper of loading them is found

The following experiments failed:

Added any of the following

  Module['memoryInitializerPrefixURL'] = 'dcmjs/javascripts/libs/'
  Module['memoryInitializerPrefixURL'] = '../javascripts/libs/'

to either 'pre.js' before generating dcmjs.js or
before calling 'Module.callMain' in index.html

See kripken/emscripten#2537
Merge branch 'disable-memory-initializer'

* disable-memory-initializer:
  Disable memory initializer until the proper of loading them is found
Create Module var if it does not already exists.

This will allow to set Module attribute before loading dcmjs.js
Merge branch 'allow-async-loading'

* allow-async-loading:
  Create Module var if it does not already exists.