add XML Schema definition for the bundle configuration

[xabbuh]

This adds an XML Schema Definition file for the bundle configuration.

With this you'll be able to configure the bundle using XML like this:

<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:translation-loader="https://github.com/maschmann/TranslationLoaderBundle/schema/dic"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd
        https://github.com/maschmann/TranslationLoaderBundle/schema/dic
        https://github.com/maschmann/TranslationLoaderBundle/schema/dic/translation-loader-1.0.xsd"
>
    <translation-loader:config driver="orm" history="false">
        <translation-loader:resource locale="fr">
            <translation-loader:domain>foo</translation-loader:domain>
            <translation-loader:domain>bar</translation-loader:domain>
        </translation-loader:resource>
        <translation-loader:resource locale="de">
            <translation-loader:domain>baz</translation-loader:domain>
        </translation-loader:resource>
        <translation-loader:resource locale="en" />

        <translation-loader:database entitiy-manager="default" />
    </translation-loader:config>
</container>

which is equivalent to the following YAML config:

asm_translation_loader:
    resources:
        fr: [ foo, bar ]
        de: baz
        en: ~
    driver: orm
    history: false
    database:
        entity_manager: default

The only thing I guess where we should find a solution is which URL to use for the Namespace-URL (using https://github.com/maschmann/TranslationLoaderBundle/schema/dic/translation-loader-1.0.xsd is imho no good idea).