Fixes #425

On some sites, loading external content can be seen problematic, so
let's provide way to disable it.

In future we might also introduce server side fetching and caching of
avatars what would make this feature less problematic.

Fixes #435

Otherwise new users have no clue what these colors mean.

Fixes #436

Fail once there would be two translations mapped into single language
code and tell user to disable SIMPLIFY_LANGUAGES in this case.

Fixes #437

In some rare cases this causes troubles as few projects translate to
both fr and fr-FR.

Issue #437

Currently translated at 40.5% (399 of 983)

Currently translated at 70.4% (693 of 983)

Currently translated at 85.9% (845 of 983)

Currently translated at 99.1% (975 of 983)

Currently translated at 38.3% (377 of 983)

Currently translated at 85.9% (845 of 983)

Currently translated at 99.0% (974 of 983)

Currently translated at 100.0% (983 of 983)

Currently translated at 37.3% (367 of 983)

Currently translated at 70.3% (692 of 983)

The error message is usually not useful at all and this code causes
false positive in current PyLint.

Currently translated at 25.2% (248 of 983)