Do not exclude root language of a regional dialect

Problem/Motivation

When I submit a translation job in German, Switzerland, I cannot pre-translate using machine translation, because it's not a language supported by many of the MT Engines.

As a workaround, I can translate the root language German, an re-upload it for German, Switzerland. But that doesn't work, because German has been excluded. The only way to re-include is to open the setting of each file individually and check the language. It's not something you want to do if you are dealing with hundres of files.

Steps to reproduce

1. Create a new translation job for a regional dialect
2. Submit the job to Crowdin
3. Try to pre-translate using any MT engine, which only supports the root language

Proposed resolution

If the root translation is not excluded, one can pre-translate the root languagae, export it and re-upload it for the regional dialect.

Remaining tasks

Create a UI to switch feature on and off

User interface changes

Checkbox to include root translation also when submitting

API changes

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Data model changes

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