New script to convert semantic domain data

This script does for semantic domain data what the Python script in
"src/scripts/language picker" does for language data: converts the data
from its original source (in this case, a set of XML files) to a JSON
format that can be picked up and dropped into and Javascript or Angular
project.

The data format for semantic domain data in Javascript will look like:

var semanticDomains_en = {
    '1.1 Sky': {
        'name': 'Sky',
        'abbreviation': '1.1',
        'description': 'Use this domain for words related to the sky.',
        'searchKeys': [
            'sky, firmament, canopy, vault',
            'air, atmosphere, airspace, stratosphere, ozone layer',
            #...
        ]
    },
    # ...
};

var semanticDomainQuestions_en = {
    '1.1 Sky': [
        'What words refer to the air around the earth? (air, atmosphere, airspace, stratosphere, ozone layer)',
        'What words are used to refer to the place or area beyond the sky? (heaven, space, outer space, ether, void, solar system)',
        # ...
    ],
    # ...
}