Display the enabled language pairs on settings page

I'm unsure about this as this might also list a lot of options that you can't actually use. Specifically, it might not tell you which of the many english or german options are the one you should enable as your service provide kind of needs to tell you that.

There are two sets of languages: supported by MemoQ (this one is very huge) and the ones that are enabled for this instance. This issue is about the ones that are enabled for particular instance that you are connected to. This will be a limited list of pair, not all that MemoQ supports, but the ones that are available for translation by user, I think this is exactly the languages that your service provider will tell you. At least it was like that with the instance I tested with.

Noted, Ben Miller also gave me the same feedback. We could consider making the getLanguages() method then be based on the language pairs, in that case this should actually automatically switch to a select and only show available options.

While checking deeper I have noticed that there is some confusing in the supported language pairs and supported remote languages. That is why I have removed memoq_languages configuration option because it is kind of a duplicate for remote_languages_mappings that is already a part of Translator entity and if plugin implements method getSupportedRemoteLanguages the provider settings form looks like this:

Attaching the updated patch

@Berdir, is there anything else that I can do here? Please let me know.